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Improved documentation
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#+TITLE: Examples
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#+STARTUP: latexpreview
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#+SETUPFILE: docs/theme.setup
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#+SETUPFILE: ./theme.setup
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* Writing nuclear coordinates
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60
docs/intro.org
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60
docs/intro.org
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#+TITLE: Motivation
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#+STARTUP: latexpreview
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#+SETUPFILE: ./theme.setup
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#+BEGIN_EXPORT html
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</td>
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<td>
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<img src="trexio_logo.png" alt="TREXIO logo"
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align="left" width="200" vspace="20" hspace="20" />
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</td></tr>
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</table>
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#+END_EXPORT
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Quantum chemistry relies on quantum mechanics to explain and predict
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the properties and behaviors of atoms, molecules, and materials.
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Although density functional theory (DFT) is one of the most widely
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used approaches thanks to its excellent ratio between computational
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cost and accuracy, another important tool is wave function theory
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(WFT), which describes the behavior of a quantum system in terms of
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its wave function.
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In order to perform WFT calculations, it is necessary to manipulate a
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large number of parameters, such as the expansion coefficients of the
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wave function and the matrix elements of the Hamiltonian operator.
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These parameters can be numerous and difficult to handle, making it
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important to have a robust and efficient method for storing and
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accessing them.
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Reproducible research remains a challenging topic, despite recent
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advances such as the introduction of the FAIR (findable, accessible,
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interoperable, reusable) data principles. A key
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aspect of reproducibility is software interoperability, which refers
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to the ability of different programs to work together and exchange
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information, allowing different systems to communicate and exchange
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data in order to function as a cohesive whole.
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Interoperable software is prevalent nowadays and is a key component of
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the Unix philosophy. In Unix shells, the most
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straightforward application of software interoperability is made
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through the use of the /pipe/ operator, where the output of a
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program is the input of another program.
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Similarly, shell scripts are created through the composition of
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smaller programs, exchanging data through files or pipes.
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A major challenge of reproducible research is the unified input/output
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(I/O) of data within a particular research domain. The Unix
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philosophy recommends the use of text files because they are
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architecture-independent, readable in any language, and can be read as
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a stream, which is useful for making programs communicate over a
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network.
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However, storing data in a text format can result in larger file sizes
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and conversion from ASCII to binary format can be computationally
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expensive for large data sets. To address this concern,
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domain-specific binary formats have been developed, such as the Joint
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Photographic Experts Group (JPEG) format for digital images
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and the Moving Picture Experts Group (MPEG) format for videos.
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These binary formats are utilized through a standardized application
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programming interface (API).
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In the field of wave function theory such a standard format and API is
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still lacking, and the purpose of the TREXIO library is to fill this gap.
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311
docs/lib.org
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311
docs/lib.org
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#+TITLE: The TREXIO library
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#+STARTUP: latexpreview
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#+SETUPFILE: ./theme.setup
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* Format specification
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#+BEGIN_EXPORT html
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</td>
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<td>
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<img src="trex_specs.png" alt="TREX in a library"
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align="right" width="300" vspace="20" hspace="20" />
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</td></tr>
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</table>
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#+END_EXPORT
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#
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The TREXIO format is designed to store all the necessary information
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to represent a wave function.
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One notable feature of TREXIO is that it is self-contained, meaning
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that all the parameters needed to recreate the wave function are
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explicitly stored within the file, eliminating the need for external
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databases. For example, instead of storing the name of a basis set
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(such as cc-pVDZ), the actual basis set parameters used in the
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calculation are stored.
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** Organization of the data
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The data in TREXIO are organized into *groups*, each containing
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multiple *attributes* defined by their *type* and *dimensions*. Each
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attribute within a group corresponds to a single scalar or array
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variable in a code. In what follows, the notation
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~<group>.<attribute>~ will be used to identify an attribute within a
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group. For example, ~nucleus.charge~ refers to the
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~charge~ attribute in the ~nucleus~ group. It is an array of type
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~float~ with dimensions ~nucleus.num~, the attribute describing the
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number of nuclei.
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** Data types
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So that TREXIO can be used in any language, we use a limited number
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of data types. The main data types are ~int~ for integers,
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~float~ for floating-point values, and ~str~ for
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character strings. For complex numbers, their real and imaginary
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parts are stored as ~float~. To minimize the risk of integer
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overflow and accuracy loss, numerical data types are stored using
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64-bit representations by default. However, in specific cases where
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integers are bounded (such as orbital indices in four-index
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integrals), the smallest possible representation is used to reduce the
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file size. The API handles any necessary type conversions.
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There are also two types derived from ~int~: ~dim~ and ~index~.
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~dim~ is used for dimensioning variables, which are positive integers
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used to specify the dimensions of an array. In the previous example,
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~nucleus.num~ is a dimensioning variable that specifies the
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dimensions of the ~nucleus.charge~ array. ~index~ is used for
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integers that correspond to array indices, because some languages
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(such as C or Python) use zero-based indexing, while others (such as
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Fortran) use one-based indexing. For convenience, values of the
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~index~ type are shifted by one when TREXIO is used in one-based
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languages to be consistent with the semantics of the language.
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You may also encounter some ~dim readonly~ variables. It means
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that the value is automatically computed and written by the TREXIO
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library, thus it is read-only and cannot be (over)written by the
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user.
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Arrays can be stored in either dense or sparse formats. If the
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sparse format is selected, the data is stored in coordinate format.
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For example, the element ~A(i,j,k,l)~ is stored as a quadruplet of
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integers $(i,j,k,l)$ along with the corresponding value. Typically,
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two-dimensional arrays are stored as dense arrays, while arrays with
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higher dimensions are stored in sparse format.
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For sparse data structures the data can be too large to fit in memory
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and the data needs to be fetched using multiple function calls to
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perform I/O on buffers. For more information on how to read/write
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sparse data structures, see the [[./examples.html][examples]].
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For the Configuration Interaction (CI) and Configuration State
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Function (CSF) groups, the ~buffered~ data type is introduced, which
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allows similar incremental I/O as for ~sparse~ data but without the
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need to write indices of the sparse values.
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For determinant lists (integer bit fields), the ~special~ attribute
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is present in the type. This means that the source code is not
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produced by the generator, but hand-written.
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Some data may be complex. In that case, the real part should be stored
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in the variable, and the imaginary part will be stored in the variable
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with the same name suffixed by ~_im~.
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* The TREXIO library
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#+BEGIN_EXPORT html
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</td>
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<td>
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<img src="trex_lib.png" alt="TREX in a library"
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align="left" width="300" vspace="20" hspace="20" />
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</td></tr>
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</table>
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#+END_EXPORT
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The TREXIO library is written is the C language, and is licensed under
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the open-source 3-clause BSD license to allow for use in all types of
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quantum chemistry software, whether commercial or not.
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The design of the library is divided into two main sections: the
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front-end and the back-end. The front-end serves as the interface
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between users and the library, while the back-end acts as the
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interface between the library and the physical storage.
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** The front-end
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By using the TREXIO library, users can store and extract data in a
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consistent and organized manner. The library provides a user-friendly
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API, including functions for reading, writing, and checking for the
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existence of data. The functions follow the pattern
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~trexio_[has|read|write]_<group>_<attribute>~, where the
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group and attribute specify the particular data being accessed. It
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also includes an error handling mechanism, in which each function call
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returns an exit code of type ~trexio_exit_code~, explaining
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the type of error.
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This can be used to catch exceptions and improve debugging in the
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upstream user application.
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To ensure the consistency of the data, the attributes can only be
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written if all the other attributes on which they explicitly depend
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have been written. For example, as the ~nucleus.coord~ array is
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dimensioned by the number of nuclei ~nucleus.num~, the ~nucleus.coord~
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attribute can only be written after ~nucleus.num~. However, the
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library is not aware of non-explicit dependencies, such as the
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relation between the electron repulsion integrals (ERIs) and MO
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coefficients. A complete control of the consistency of the data is
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therefore impossible, so the attributes were chosen to be by default
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/immutable/. By only allowing data to be written only once, the
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risk of modifying data in a way that creates inconsistencies is
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reduced. For example, if the ERIs have already been written, it would
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be inconsistent to later modify the MO coefficients. To allow for
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flexibility, the library also allows for the use of an /unsafe/
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mode, in which data can be overwritten. However, this mode carries
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the risk of producing inconsistent files, and the ~metadata~ group's
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~unsafe~ attribute is set to ~1~ to indicate that the file has
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potentially been modified in a dangerous way. This attribute can be
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manually reset to ~0~ if the user is confident that the modifications
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made are safe.
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** The back-end
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At present, TREXIO supports two back-ends: one relying only on the
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C standard library to produce plain text files (the so-called /text/
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back-end), and one relying on the HDF5 library.
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With the text back-end, the TREXIO "file" is a directory containing
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multiple text files, one for each group. This back end is intended
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to be used in development environments, as it gives access to the
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user to the standard tools such as ~diff~ and ~grep~.
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In addition, text files are better adapted than binary files for
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version control systems such as Git, so this format can be also
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used for storing reference data for unit tests.
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HDF5 is a binary file format and library for storing and managing
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large amounts of data in a hierarchical structure. It allows users
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to manipulate data in a way similar to how files and directories
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are manipulated within the file system. The HDF5 library provides
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optimal performance through its memory mapping mechanism and
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supports advanced features such as serial and parallel I/O,
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chunking, and compression filters. However, HDF5 files are in
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binary format, which requires additional tools such as ~h5dump~ to
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view them in a human-readable format. It is widely used in
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scientific and engineering applications, and is known for its high
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performance and ability to handle large data sets efficiently.
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The TREXIO HDF5 back-end is the recommended choice for production
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environments, as it provides high I/O performance. Furthermore,
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all data is stored in a single file, making it especially suitable
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for parallel file systems like Lustre. These file systems are
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optimized for large, sequential I/O operations and are not
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well-suited for small, random I/O operations. When multiple small
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files are used, the file system may become overwhelmed with
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metadata operations like creating, deleting, or modifying files,
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which can adversely affect performance.
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In a benchmarking program designed to compare the two back-ends of
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the library, the HDF5 back-end was found to be significantly faster
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than the text back-end. The program wrote a wave function made up
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of 100 million Slater determinants and measured the time taken to
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write the Slater determinants and CI coefficients. The HDF5
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back-end achieved a speed of $10.4\times10^6$ Slater determinants
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per second and a data transfer rate of 406 MB/s, while the text
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back-end had a speed of $1.1\times10^6$ determinants per second and
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a transfer rate of 69 MB/s. These results were obtained on a DELL
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960 GB mix-use solid-state drive (SSD). The HDF5 back-end was able
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to achieve a performance level close to the peak performance of the
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SSD, while the text back-end's performance was limited by the speed
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of the CPU for performing binary to ASCII conversions.
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In addition to the HDF5 and text back-ends, it is also possible to
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introduce new back-ends to the library. For example, a back-end
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could be created to support object storage systems, such as those
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used in cloud-based applications or for archiving in open data
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repositories.
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** Supported languages
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One of the main benefits of using C as the interface for a library is
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that it is easy to use from other programming languages. Many
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programming languages, such as Python or Julia, provide built-in
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support for calling C functions, which means that it is relatively
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straightforward to write a wrapper that allows a library written in C
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to be called from another language.
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In general, libraries with a C interface are the easiest to use from
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other programming languages, because C is widely supported and has a
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simple, stable application binary interface (ABI). Other languages,
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such as Fortran and C++, may have more complex ABIs and may
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require more work to interface with them.
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TREXIO has been employed in codes developed in various programming
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languages, including C, C++, Fortran, Python, OCaml, and Julia. While
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Julia is designed to enable the use of C functions without the need
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for additional manual interfacing, the TREXIO C header file was
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automatically integrated into Julia programs using the
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~CBindings.jl~ package.
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In contrast, specific bindings have been provided for Fortran, Python,
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and OCaml to simplify the user experience.
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In particular, the binding for Fortran is not distributed as multiple
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compiled Fortran module files (~.mod~), but instead as a single
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Fortran source file (~.F90~). The distribution of the source file
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instead of the compiled module has multiple benefits. It ensures that
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the TREXIO module is always compiled with the same compiler as the
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client code, avoiding the compatibility problem of ~.mod~ files
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between different compiler versions and vendors. The single-file
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model requires very little changes in the build system of the user's
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codes, and it facilitates the search for the interface of a particular
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function. In addition, advanced text editors can parse the TREXIO
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interface to propose interactive auto-completion of the TREXIO
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function names to the developers.
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Finally, the Python module, partly generated with SWIG and fully
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compatible with NumPy, allows Python users to interact with the
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library in a more intuitive and user-friendly way. Using the Python
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interface is likely the easiest way to begin using TREXIO and
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understanding its features. In order to help users get started with
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TREXIO and understand its functionality, tutorials in Jupyter
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notebooks are available on GitHub
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(https://github.com/TREX-CoE/trexio-tutorials), and can be executed
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via the Binder platform.
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** Source code generation and documentation
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Source code generation is a valuable technique that can significantly
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improve the efficiency and consistency of software development. By
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using templates to generate code automatically, developers can avoid
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manual coding and reduce the risk of errors or inconsistencies. This
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approach is particularly useful when a large number of functions
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follow similar patterns, as in the case of the TREXIO library, where
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functions are named according to the pattern
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~trexio_[has|read|write]_<group>_<attribute>~.
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By generating these functions from the format specification using
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templates, the developers can ensure that the resulting code follows a
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consistent structure and is free from errors or inconsistencies.
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The description of the format is written in a text file in the Org
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format. Org is a structured plain text format, containing information
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expressed in a lightweight markup language similar to the popular
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Markdown language. While Org was introduced as a mode of the GNU
|
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Emacs text editor, its basic functionalities have been implemented in
|
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most text editors such as Vim, Atom or VS Code.
|
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|
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There are multiple benefits in using the Org format. The first
|
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benefit is that the Org syntax is easy to learn and allows for the
|
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insertion of equations in \LaTeX{} syntax. Additionally, Org files
|
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can be easily converted to HyperText Markup Language (HTML) or
|
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Portable Document Format (PDF) for generating documentation. The
|
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second benefit is that GNU Emacs is a programmable text editor and
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code blocks in Org files can be executed interactively, similar to
|
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Jupyter notebooks. These code blocks can also manipulate data defined
|
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in tables and this feature is used to automatically transform tables
|
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describing groups and attributes in the documentation into a
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JavaScript Object Notation (JSON) file.
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This JSON file is then used by a Python script to generate the needed
|
||||
functions in C language, as well as header files and some files
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required for the Fortran, Python, and OCaml interfaces.
|
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|
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With this approach, contributions to the development of the TREXIO
|
||||
library can be made simply by adding new tables to the Org file, which
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can be submitted as /pull requests/ on the project's GitHub
|
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repository (https://github.com/trex-coe/trexio). Overall, this
|
||||
process allows for a more efficient and consistent development process
|
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and enables contributions from a wider range of individuals,
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regardless of their programming skills.
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|
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** Availability
|
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|
||||
The TREXIO library is designed to be portable and easy to install
|
||||
on a wide range of systems. It follows the C99 standard to ensure
|
||||
compatibility with older systems, and can be configured with either
|
||||
the GNU Autotools or the CMake build systems. The only external
|
||||
dependency is the HDF5 library, which is widely available on HPC
|
||||
platforms and as packages on major Linux distributions. Note that
|
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it is possible to disable the HDF5 back-end at configuration time,
|
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allowing TREXIO to operate only with the text back-end and have
|
||||
zero external dependencies. This can be useful for users who may
|
||||
not be able to install HDF5 on certain systems.
|
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|
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TREXIO is distributed as a tarball containing the source code,
|
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generated code, documentation, and Fortran interface. It is also
|
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available as a binary ~.deb~ package for Debian-based Linux
|
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distributions and as packages for Guix, Spack and Conda. The Python
|
||||
module can be found in the PyPI repository, the OCaml binding is
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available in the official OPAM repository, and the ~.deb~ packages
|
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are available in Ubuntu 23.04.
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@ -1,11 +1,11 @@
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# -*- mode: org; -*-
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#+HTML_LINK_HOME: index.html
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#+OPTIONS: H:4 num:t toc:t \n:nil @:t ::t |:t ^:t -:t f:t *:t <:t d:(HIDE)
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#+OPTIONS: H:4 num:t toc:nil \n:nil @:t ::t |:t ^:t -:t f:t *:t <:t d:(HIDE)
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####### #+SETUPFILE: ../docs/org-html-themes/org/theme-readtheorg.setup
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#+INFOJS_OPT: toc:t mouse:underline path:org-info.js
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#+INFOJS_OPT: mouse:underline path:org-info.js
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#+HTML_HEAD: <link rel="stylesheet" title="Standard" href="trexio.css" type="text/css" />
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#+STARTUP: align nodlcheck hidestars oddeven lognotestate
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BIN
docs/trex_lib.png
Normal file
BIN
docs/trex_lib.png
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After Width: | Height: | Size: 1.6 MiB |
BIN
docs/trex_specs.png
Normal file
BIN
docs/trex_specs.png
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After Width: | Height: | Size: 1.5 MiB |
BIN
docs/trexio.png
Normal file
BIN
docs/trexio.png
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Binary file not shown.
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After Width: | Height: | Size: 425 KiB |
BIN
docs/trexio_logo.png
Normal file
BIN
docs/trexio_logo.png
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Binary file not shown.
|
After Width: | Height: | Size: 37 KiB |
@ -2,34 +2,57 @@
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#+PROPERTY: comments org
|
||||
#+SETUPFILE: ../docs/theme.setup
|
||||
|
||||
--------------------------------
|
||||
#+BEGIN_EXPORT html
|
||||
<script async src="https://cse.google.com/cse.js?cx=a67f8ab65a66f97f2"></script>
|
||||
<div class="gcse-search"></div>
|
||||
#+END_EXPORT
|
||||
--------------------------------
|
||||
|
||||
------------------
|
||||
TREXIO is an open-source file format and library developed for the storage and
|
||||
manipulation of data produced by quantum chemistry calculations. It was
|
||||
designed with the goal of providing a reliable and efficient method of storing
|
||||
and exchanging wave function parameters and matrix elements.
|
||||
|
||||
- [[./tutorial_benzene.html][Tutorial]]
|
||||
The library consists of a front-end implemented in the C programming language
|
||||
and two different back-ends: a text back-end and a binary back-end utilizing
|
||||
the HDF5 library enabling fast read and write speeds. It is compatible with a
|
||||
variety of platforms and has interfaces for Fortran, Python, and OCaml.
|
||||
|
||||
--------------------------------
|
||||
|
||||
#+BEGIN_EXPORT html
|
||||
<table style="width:100%">
|
||||
<tr><td style="width:50%">
|
||||
#+END_EXPORT
|
||||
|
||||
- [[./intro.html][Motivation]]
|
||||
- [[./lib.html][The TREXIO library]]
|
||||
- [[./trex.html][Data stored with TREXIO]]
|
||||
- [[./tutorial_benzene.html][Tutorial]]
|
||||
- [[./examples.html][How-to guide]]
|
||||
- [[./templator_front.html][Front end API]]
|
||||
- [[./templator_hdf5.html][HDF5 back end]]
|
||||
- [[./templator_text.html][TEXT back end]]
|
||||
|
||||
#+BEGIN_EXPORT html
|
||||
</td>
|
||||
<td>
|
||||
<img src="trexio.png" alt="T-Rex talking about chemistry"
|
||||
align="right" width="300"/>
|
||||
</td></tr>
|
||||
</table>
|
||||
#+END_EXPORT
|
||||
|
||||
--------------------------------
|
||||
|
||||
|
||||
The TREXIO library defines a standard format for storing wave functions,
|
||||
together with an C-compatible API such that it can be easily used in any
|
||||
programming language.
|
||||
|
||||
|
||||
The source code of the library is available at
|
||||
https://github.com/trex-coe/trexio
|
||||
and bug reports should be submitted at
|
||||
https://github.com/trex-coe/trexio/issues.
|
||||
|
||||
The TREXIO library is licensed under the open-source 3-clause BSD license.
|
||||
|
||||
------------------
|
||||
|
||||
[[https://trex-coe.eu/sites/default/files/inline-images/euflag.jpg]] [[https://trex-coe.eu][TREX: Targeting Real Chemical Accuracy at the Exascale]] project has received funding from the European Union’s Horizon 2020 - Research and Innovation program - under grant agreement no. 952165. The content of this document does not represent the opinion of the European Union, and the European Union is not responsible for any use that might be made of such content.
|
||||
|
||||
@ -81,7 +81,7 @@ function extract_doc()
|
||||
${org} \
|
||||
--load ${CONFIG_TANGLE} \
|
||||
-f org-html-export-to-html &> /dev/null
|
||||
mv ${local_html} ${DOCS}
|
||||
mv -f ${local_html} ${DOCS}
|
||||
rm -f "${local_html}~"
|
||||
|
||||
}
|
||||
@ -99,7 +99,7 @@ function main() {
|
||||
# Create documentation
|
||||
cd ${SRC}
|
||||
|
||||
for dir in ${SRC}/templates_*/ ${TREXIO_ROOT}/
|
||||
for dir in ${SRC}/templates_*/ ${TREXIO_ROOT}/ ${TREXIO_ROOT}/docs
|
||||
do
|
||||
dir=${dir%*/}
|
||||
echo ${dir}
|
||||
|
||||
55
trex.org
55
trex.org
@ -1,54 +1,13 @@
|
||||
#+TITLE: TREX Configuration file
|
||||
#+TITLE: Data stored in TREXIO
|
||||
#+STARTUP: latexpreview
|
||||
#+SETUPFILE: docs/theme.setup
|
||||
|
||||
This page contains information about the general structure of the
|
||||
TREXIO library. The source code of the library can be automatically
|
||||
generated based on the contents of the ~trex.json~ configuration file,
|
||||
which itself is generated from different sections (groups) presented
|
||||
below.
|
||||
|
||||
All quantities are saved in TREXIO files in atomic units. The
|
||||
dimensions of the arrays in the tables below are given in column-major
|
||||
order (as in Fortran), and the ordering of the dimensions is reversed
|
||||
in the produced ~trex.json~ configuration file as the library is
|
||||
written in C.
|
||||
|
||||
TREXIO currently supports ~int~, ~float~ and ~str~ types for both
|
||||
single attributes and arrays. Note, that some attributes might have
|
||||
~dim~ type (e.g. ~num~ of the ~nucleus~ group). This type is treated
|
||||
exactly in the same way as ~int~ with the only difference that ~dim~
|
||||
variables cannot be negative. This additional constraint is required
|
||||
because ~dim~ attributes are used internally to allocate memory and to
|
||||
check array boundaries in the memory-safe API. Most of the times, the
|
||||
~dim~ variables contain the ~num~ suffix.
|
||||
You may also encounter some ~dim readonly~ variables.
|
||||
It means that the value is automatically computed and written by the
|
||||
TREXIO library, thus it is read-only and cannot be (over)written by the
|
||||
user.
|
||||
|
||||
In Fortran, arrays are 1-based and in most other languages the
|
||||
arrays are 0-based. Hence, we introduce the ~index~ type which is a
|
||||
1-based ~int~ in the Fortran interface and 0-based otherwise.
|
||||
|
||||
For sparse data structures such as electron replusion integrals,
|
||||
the data can be too large to fit in memory and the data needs to be
|
||||
fetched using multiple function calls to perform I/O on buffers.
|
||||
For more information on how to read/write sparse data structures, see
|
||||
the [[./examples.html][examples]]. The ~sparse~ data representation implies the
|
||||
[[https://en.wikipedia.org/wiki/Sparse_matrix#Coordinate_list_(COO)][coordinate list]] representation, namely the user has to write a list
|
||||
of indices and values.
|
||||
|
||||
For the Configuration Interaction (CI) and Configuration State Function (CSF)
|
||||
groups, the ~buffered~ data type is introduced, which allows similar incremental
|
||||
I/O as for ~sparse~ data but without the need to write indices of the sparse values.
|
||||
|
||||
For determinant lists (integer bit fields), the ~special~ attribute is present in the type.
|
||||
This means that the source code is not produced by the generator, but hand-written.
|
||||
|
||||
Some data may be complex. In that case, the real part should be stored
|
||||
in the variable, and the imaginary part will be stored in the variable
|
||||
with the same name suffixed by ~_im~.
|
||||
For simplicity, the singular form is always used for the names of
|
||||
groups and attributes, and all data are stored in atomic units.
|
||||
The dimensions of the arrays in the tables below are given in
|
||||
column-major order (as in Fortran), and the ordering of the dimensions
|
||||
is reversed in the produced ~trex.json~ configuration file as the
|
||||
library is written in C.
|
||||
|
||||
#+begin_src python :tangle trex.json :exports none
|
||||
{
|
||||
|
||||
Loading…
Reference in New Issue
Block a user