mirror of
https://github.com/triqs/dft_tools
synced 2024-12-27 06:43:40 +01:00
3fe400d34c
- examples split from the rst file using a python script (split_code). - Final result for the doc is unchanged. - examples are compiled and tested with the other tests. - examples' code have been clang-formatted, with triqs style. - doc compiles much faster, and with the same options as the rest of the test. - examples are added as tests, so they are run by make test, as simple C tests. - done for the tutorials and the reference. - autocompile removed (changed into triqs_example directive). - add triqs_example : - make a literal include of the source code. - runs the compiled example - add, as before, the result to the source code in the doc. - added the script split_code, used to make the changes automatically, maybe for later reuse. (in _tools)
54 lines
1.7 KiB
ReStructuredText
54 lines
1.7 KiB
ReStructuredText
|
|
.. highlight:: c
|
|
|
|
Evaluating CLEF expressions
|
|
===============================
|
|
|
|
Forming expressions is nice, but completely useless unless one can *evaluate* them
|
|
by affecting some values to the placeholder and actually *do* the computation.
|
|
|
|
Expressions are evaluated with the eval function ::
|
|
|
|
eval ( expression , placeholder_1 = value_1, placeholder_2 = value_2, ...)
|
|
|
|
The evaluation can be :
|
|
|
|
* *complete* : when a value has been affected to every placeholder, so the result is not
|
|
an expression any more, but the result of the computation....
|
|
|
|
* *partial* : when some placeholder are still free (no value has been affected to them).
|
|
The result is another expression where the parts that could be computed have been computed.
|
|
|
|
Complete evaluation
|
|
--------------------
|
|
|
|
.. triqs_example:: ./expressions_eval_0.cpp
|
|
Note that :
|
|
|
|
* The order of placeholder does not matter in calling eval.
|
|
* It is an error to put the same placeholder twice.
|
|
* The correct version of eval is found by ADL (Argument Dependent Lookup) in the triqs::clef namespace.
|
|
|
|
Partial evaluation
|
|
--------------------
|
|
|
|
The evaluation can also be partial, in which case the compiler replaces the placeholder whose value is provided
|
|
and rebuild a new expression tree.
|
|
|
|
Example ::
|
|
|
|
auto e1 = x_ + 2*y_;
|
|
// return type ---> value
|
|
auto r = eval( e1 , x_ =1); // expression ---> 1 + (2 * y_)
|
|
auto e2 = eval( e1 , x_ =x_ + y_); // expression ---> ((x_ + y_) + (2 * y_))
|
|
auto r = eval( e2, x_ = 1, y_ = 2); // int ---> 7
|
|
|
|
During the partial evaluation, all subtrees that can evaluated are evaluated.
|
|
For example ::
|
|
|
|
eval(x_ + f(y_) , y_=1); // --> x + f(1)
|
|
|
|
In this case, the function f is called by eval.
|
|
|
|
|