mirror of
https://github.com/triqs/dft_tools
synced 2024-12-26 14:23:38 +01:00
f7fad85fca
This is an iteration over the doc mainly thank to Priyanka. I fixed another couple of details on the way.
73 lines
2.7 KiB
ReStructuredText
73 lines
2.7 KiB
ReStructuredText
.. highlight:: c
|
|
|
|
|
|
Motivation : a little tour of CLEF
|
|
=====================================
|
|
|
|
As usual, the best is to start with a few examples, to show the library in action.
|
|
|
|
|
|
.. compileblock::
|
|
|
|
#include <triqs/clef.hpp>
|
|
#include <triqs/arrays.hpp>
|
|
#include <iostream>
|
|
#include <algorithm>
|
|
int main() {
|
|
// Declaring some placeholders (i.e. dummy variables).
|
|
triqs::clef::placeholder <0> i_;
|
|
triqs::clef::placeholder <1> j_;
|
|
|
|
// Declaring a 3x3 matrix
|
|
triqs::arrays::matrix<double> A (3,3);
|
|
|
|
// Automatically filling the matrix
|
|
// -> forget about the bounds, it is automatic
|
|
// -> forget about the best order to order the for loops for performance, it is also automatic
|
|
A(i_,j_) << i_ + 2*j_;
|
|
|
|
// Cheking the result
|
|
std::cout<< A<< std::endl;
|
|
|
|
// It also works for std container: we just have to add a call clef::make_expr function
|
|
std::vector<double> V(10);
|
|
double pi = std::acos(-1);
|
|
|
|
// Automatically filling the vector with the evaluation of the expression in i_
|
|
triqs::clef::make_expr(V) [i_] << cos( 2* pi / 5.0 * i_ );
|
|
|
|
// -> by the way, the constant calculation is precomputed
|
|
// (expressions are partially evaluated as soon as possible)
|
|
// illustration :
|
|
// the time_consuming_function will be called only once in the loop, while cos is called 10 times
|
|
auto time_consuming_function=[](double x){std::cout<<"call time_consuming_function"<<std::endl;return 2*x;};
|
|
triqs::clef::make_expr(V) [i_] << cos( time_consuming_function(10) * i_ );
|
|
|
|
// If you insist using on more complex containers...
|
|
std::vector<std::vector<double>> W(3, std::vector<double>(5));
|
|
triqs::clef::make_expr(W)[i_] [j_] << i_ + cos( time_consuming_function(10) * j_ + i_);
|
|
|
|
// You can also put a CLEF expression in a std::function
|
|
// a function i -> 2*i +1
|
|
std::function<int(int)> f = i_ >> 2*i_ +1;
|
|
// a function (i,j) -> 2*i +j
|
|
std::function<double(int,int)> g = var(i_,j_) >> 2*i_ +j_;
|
|
// checking ...
|
|
std::cout<< "f(10) =" << f(10)<< " g(1,2) =" << g(1,2)<< std::endl;
|
|
|
|
// You can also use a Curry form : h is a function i-> j -> 2*i+ j
|
|
auto h = i_ >> (j_ >> 2*i_ +j_);
|
|
std::cout<< "h(1)(2) = " << h(1)(2) << std::endl;
|
|
|
|
// You an also use this to quickly write some lambda, as an alternative syntax to the C++ lambda
|
|
// with e.g. STL algorithms (with the advantage that the function is polymorphic!).
|
|
std::vector<int> v = {0,-1,2,-3,4,5,-6};
|
|
// replace all negative elements (i.e. those for which i -> (i<0) return true), by 0
|
|
std::replace_if(begin(v), end(v), i_ >> (i_<0), 0);
|
|
// for non believer, it really worked ...
|
|
for (auto const & x : v) std::cout <<x <<" "; std::cout << std::endl;
|
|
}
|
|
|
|
|
|
|