mirror of
https://github.com/triqs/dft_tools
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145 lines
3.7 KiB
ReStructuredText
145 lines
3.7 KiB
ReStructuredText
.. highlight:: c
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.. _arr_call:
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Operator()
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==================================
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**Synopsis** ::
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value_type const & operator()(size_t ...) const (1a)
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value_type & operator()(size_t ...) (1b)
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view_type operator()() const (2a)
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view_type operator()( size_t | range | ellipsis ) const (2b)
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`clef expression` operator()( `at least a lazy argument` ) const (3)
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This is valid for both the container (e.g. array), and the view (e.g. array_view).
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.. _arr_element_access:
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(1) Element access
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---------------------------------
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Following the concept :ref:`ImmutableCuboidArray`, the form (1) is an access to the elements.
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It must be called with exactly `rank` size_t (or it is a compile time error).
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Example
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^^^^^^^^^
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.. compileblock::
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#include <triqs/arrays.hpp>
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using namespace triqs::arrays;
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int main(){
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array<double,2> A(2,3);
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A() = 0; // assign 0 to A
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A(0,0) = 5;
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A(1,1) = 2 * A(0,0);
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std::cout <<"A = "<< A << std::endl;
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}
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Another ::
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A(1, range(0,2) ) // 1d slice
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A(1, range()) // 1d slice taking all the second dim
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A(range(0,10,2), range(0,10,2)) // a 2d slice viewing every each elements with even coordinates.
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array_view<T,1> SL = A(0,range(0,3)); // naming the view. No data copied here !
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array_view<T,1> SL ( A(0,range(0,3))); // same thing !
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.. _arr_making_view:
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(2) Building a view
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---------------------------------
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When the arguments contains at least one :ref:`range<arr_range>` or one :ref:`ellipsis<arr_ellipsis>`, and no placeholder (see 3)),
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the return type is a (partial) view of the container.
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The special case (2a) (no argument) returns a complete view of the object
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(equivalent to view_type(* this)).
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The return type of the () operator is :
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* Partial views of array or array_view return a array_view.
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* Partial views of vector or vector_view return a vector_view.
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* 2d partial views of matrix or matrix_view return a matrix_view.
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* BUT : (1d) partial view of matrix or matrix_view return a vector_view.
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Example
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^^^^^^^^^^^^
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.. compileblock::
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#include <triqs/arrays.hpp>
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using namespace triqs::arrays;
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int main(){
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array<double,2> A(4,4);
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for(int i=0; i<4; ++i) for(int j=0; j<4; ++j) A(i,j) = i+ 10*j;
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array_view<double,2> V = A(range(0,2), range(0,2));
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std::cout <<"V = "<< V << std::endl;
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V = -V;
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std::cout <<"A = "<< A << std::endl;
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}
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.. toctree::
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:hidden:
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range_ell
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.. highlight:: c
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.. _arr_lazy:
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(3) Interaction with clef expressions
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-------------------------------------------------
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* The containers and their views can be used with the triqs::clef library :
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* Using the clef library offers a quick and efficient way to fill an array with multiple advantages :
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* It is simpler and more readeable than a series of for loops.
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* It is usually more optimal since the for loops are automatically written in the TraversalOrder of the
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array.
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* NB : the expression can be (and are) inlined by the compilers...
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* **Example** :
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.. compileblock::
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#include <triqs/arrays.hpp>
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using triqs::arrays::array; using triqs::clef::placeholder;
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int main(){
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placeholder<0> i_; placeholder<1> j_;
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array<double,2> A(2,2), B(2,2);
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A(i_,j_) << i_ + 2*j_ ;
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B(i_,j_) << A(j_,i_)/2;
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std::cout << "A = "<<A << std::endl;
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std::cout << "B = "<<B << std::endl;
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}
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.. note::
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The syntax uses a <<, not = since the array is not assigned to an expression
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but filled by the evaluation thereof.
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