third_party/boost/numeric/ublas/examples/tensor/construction_access.cpp

//
//  Copyright (c) 2018-2019, Cem Bassoy, cem.bassoy@gmail.com
//
//  Distributed under the Boost Software License, Version 1.0. (See
//  accompanying file LICENSE_1_0.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt)
//
//  The authors gratefully acknowledge the support of
//  Fraunhofer IOSB, Ettlingen, Germany
//

#include <boost/numeric/ublas/tensor.hpp>
#include <boost/multiprecision/cpp_bin_float.hpp>

#include <ostream>

int main()
{
	using namespace boost::numeric::ublas;
	using namespace boost::multiprecision;	


	// creates a three-dimensional tensor with extents 3,4 and 2
	// tensor A stores single-precision floating-point number according
	// to the first-order storage format
	using ftype = float;
	auto A = tensor<ftype>{3,4,2};

	// initializes the tensor with increasing values along the first-index
	// using a single index.
	auto vf = ftype(0);
	for(auto i = 0u; i < A.size(); ++i, vf += ftype(1))
		A[i] = vf;

	// formatted output
	std::cout << "% --------------------------- " << std::endl;
	std::cout << "% --------------------------- " << std::endl << std::endl;
	std::cout << "A=" << A << ";" << std::endl << std::endl;

	// creates a four-dimensional tensor with extents 5,4,3 and 2
	// tensor A stores complex floating-point extended double precision numbers
	// according to the last-order storage format
	// and initializes it with the default value.
	using ctype = std::complex<cpp_bin_float_double_extended>;
	auto B = tensor<ctype,last_order>(shape{5,4,3,2},ctype{});

	// initializes the tensor with increasing values along the last-index
	// using a single-index
	auto vc = ctype(0,0);
	for(auto i = 0u; i < B.size(); ++i, vc += ctype(1,1))
		B[i] = vc;

	// formatted output
	std::cout << "% --------------------------- " << std::endl;
	std::cout << "% --------------------------- " << std::endl << std::endl;
	std::cout << "B=" << B << ";" << std::endl << std::endl;



	auto C = tensor<ctype,last_order>(B.extents());
	// computes the complex conjugate of elements of B
	// using multi-index notation.
	for(auto i = 0u; i < B.size(0); ++i)
		for(auto j = 0u; j < B.size(1); ++j)
			for(auto k = 0u; k < B.size(2); ++k)
				for(auto l = 0u; l < B.size(3); ++l)
					C.at(i,j,k,l) = std::conj(B.at(i,j,k,l));

	std::cout << "% --------------------------- " << std::endl;
	std::cout << "% --------------------------- " << std::endl << std::endl;
	std::cout << "C=" << C << ";" << std::endl << std::endl;


	// computes the complex conjugate of elements of B
	// using iterators.
	auto D = tensor<ctype,last_order>(B.extents());
	std::transform(B.begin(), B.end(), D.begin(), [](auto const& b){ return std::conj(b); });
	std::cout << "% --------------------------- " << std::endl;
	std::cout << "% --------------------------- " << std::endl << std::endl;
	std::cout << "D=" << D << ";" << std::endl << std::endl;

	// reshaping tensors.
	auto new_extents = B.extents().base();
	std::next_permutation( new_extents.begin(), new_extents.end() );
	D.reshape( shape(new_extents)  );
	std::cout << "% --------------------------- " << std::endl;
	std::cout << "% --------------------------- " << std::endl << std::endl;
	std::cout << "newD=" << D << ";" << std::endl << std::endl;
}