mirror of
https://github.com/triqs/dft_tools
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57 lines
2.1 KiB
C++
57 lines
2.1 KiB
C++
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#include <triqs/clef.hpp>
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#include <triqs/clef/io.hpp>
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// a general implementation type for all domain and summation methods
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template<typename Domain, typename Options> struct sum_impl;
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struct Riemann{}; // one sum method
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template<typename Domain> struct sum_impl<Domain, Riemann> {
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Domain d;
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sum_impl(Domain const &d_):d(d_) {}
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// Disabled when F is a lazy_expression
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template <typename F>
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typename std::enable_if< !triqs::clef::is_any_lazy <F>::value, double >::type
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operator() (F const & f) const { double s=0; for (int u=0; u<10; ++u) s += f(u/10.0); return s;}
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// Defines operator(). Enabled iff one argument is a clef expression.
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template< typename... Args>
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typename triqs::clef::result_of::make_expr_call<sum_impl,Args...>::type
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operator()( Args&&... args ) const { return triqs::clef::make_expr_call (*this,args...);}
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// How to print this object in the printing of clef expression
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friend std::ostream & operator<<(std::ostream & out, sum_impl const & x) { return out<<"sum";}
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};
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template<typename Domain, typename Option>
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sum_impl<Domain,Option> sum_functional (Domain && d, Option) {return d;}
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//--------- MAIN ---------------------------------------
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struct DOM{};
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int main() {
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// two placeholders
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triqs::clef::placeholder <1> x_;
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triqs::clef::placeholder <2> y_;
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DOM d; // a domain
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// integrate_on_d is the integration (!) over d with Riemann method
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auto integrate_on_d = sum_functional( d, Riemann());
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// This is a simple application of the sum to a function
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std::cout<< integrate_on_d( x_ >> 2*x_ + 1 ) << std::endl;
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// This creates a clef expression of placeholder y_, waiting to make the sum
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// Indeed the argument is a clef expression of y_ returning a function
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// composed by integrate_on_d, it is a clef expression of y_ returning a double
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std::cout<< integrate_on_d( x_ >> 2*x_ + 1 + y_ ) << std::endl;
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// Of course this expression can be mixed with others...
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std::cout<< y_ + 2* integrate_on_d( x_ >> 2*x_ + 1 + y_ ) << std::endl;
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// and it can be evaluated
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std::cout<< eval (y_ + 2* integrate_on_d( x_ >> 2*x_ + 1 + y_ ) ,y_ =0) << std::endl;
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}
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