blas2.cpp

In this tutorial the BLAS level 2 functionality in ViennaCL is demonstrated.

We start with including the required header files:

// System headers
#include <iostream>

// uBLAS headers
#include <boost/numeric/ublas/io.hpp>
#include <boost/numeric/ublas/triangular.hpp>
#include <boost/numeric/ublas/matrix_sparse.hpp>
#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/matrix_proxy.hpp>
#include <boost/numeric/ublas/vector_proxy.hpp>
#include <boost/numeric/ublas/lu.hpp>
#include <boost/numeric/ublas/io.hpp>


// Must be set if you want to use ViennaCL algorithms on ublas objects
#define VIENNACL_WITH_UBLAS 1

// ViennaCL headers
#include "viennacl/scalar.hpp"
#include "viennacl/vector.hpp"
#include "viennacl/matrix.hpp"
#include "viennacl/linalg/direct_solve.hpp"
#include "viennacl/linalg/prod.hpp"       //generic matrix-vector product
#include "viennacl/linalg/norm_2.hpp"     //generic l2-norm for vectors
#include "viennacl/linalg/lu.hpp"         //LU substitution routines
#include "viennacl/tools/random.hpp"

// Make `boost::numeric::ublas` available under the shortcut `ublas`:
using namespace boost::numeric;

We do not need any auxiliary functions in this example, so let us start directly in main():

int main()
{
  typedef float       ScalarType;

  viennacl::tools::uniform_random_numbers<ScalarType> randomNumber;

Set up some uBLAS vectors and a matrix. They will be later used for filling the ViennaCL objects with data.

ublas::vector<ScalarType> rhs(12);
for (unsigned int i = 0; i < rhs.size(); ++i)
  rhs(i) = randomNumber();
ublas::vector<ScalarType> rhs2 = rhs;
ublas::vector<ScalarType> result = ublas::zero_vector<ScalarType>(10);
ublas::vector<ScalarType> result2 = result;
ublas::vector<ScalarType> rhs_trans = rhs;
rhs_trans.resize(result.size(), true);
ublas::vector<ScalarType> result_trans = ublas::zero_vector<ScalarType>(rhs.size());

ublas::matrix<ScalarType> matrix(result.size(),rhs.size());

Fill the uBLAS-matrix

for (unsigned int i = 0; i < matrix.size1(); ++i)
  for (unsigned int j = 0; j < matrix.size2(); ++j)
    matrix(i,j) = randomNumber();

Use some plain STL types:

std::vector< ScalarType > stl_result(result.size());
std::vector< ScalarType > stl_rhs(rhs.size());
std::vector< std::vector<ScalarType> > stl_matrix(result.size());
for (unsigned int i=0; i < result.size(); ++i)
{
  stl_matrix[i].resize(rhs.size());
  for (unsigned int j = 0; j < matrix.size2(); ++j)
  {
    stl_rhs[j] = rhs[j];
    stl_matrix[i][j] = matrix(i,j);
  }
}

Set up some ViennaCL objects (initialized with zeros) and then copy data from the uBLAS objects.

viennacl::vector<ScalarType> vcl_rhs(rhs.size());
viennacl::vector<ScalarType> vcl_result(result.size());
viennacl::matrix<ScalarType> vcl_matrix(result.size(), rhs.size());
viennacl::matrix<ScalarType> vcl_matrix2(result.size(), rhs.size());

viennacl::copy(rhs.begin(), rhs.end(), vcl_rhs.begin());
viennacl::copy(matrix, vcl_matrix);     //copy from ublas dense matrix type to ViennaCL type

Some basic matrix operations with ViennaCL are as follows:

vcl_matrix2 = vcl_matrix;
vcl_matrix2 += vcl_matrix;
vcl_matrix2 -= vcl_matrix;
vcl_matrix2 = vcl_matrix2 + vcl_matrix;
vcl_matrix2 = vcl_matrix2 - vcl_matrix;

viennacl::scalar<ScalarType> vcl_3(3.0);
vcl_matrix2 *= ScalarType(2.0);
vcl_matrix2 /= ScalarType(2.0);
vcl_matrix2 *= vcl_3;
vcl_matrix2 /= vcl_3;

A matrix can be cleared directly:

vcl_matrix.clear();

Other ways of data transfers between matrices in main memory and a ViennaCL matrix:

viennacl::copy(stl_matrix, vcl_matrix); //alternative: copy from STL vector< vector<> > type to ViennaCL type

//for demonstration purposes (no effect):
viennacl::copy(vcl_matrix, matrix); //copy back from ViennaCL to ublas type.
viennacl::copy(vcl_matrix, stl_matrix); //copy back from ViennaCL to STL type.

Matrix-Vector Products

Compute matrix-vector products

std::cout << "----- Matrix-Vector product -----" << std::endl;
result = ublas::prod(matrix, rhs);                            //the ublas way
stl_result = viennacl::linalg::prod(stl_matrix, stl_rhs);     //using STL
vcl_result = viennacl::linalg::prod(vcl_matrix, vcl_rhs);     //the ViennaCL way

Compute transposed matrix-vector products

std::cout << "----- Transposed Matrix-Vector product -----" << std::endl;
result_trans = prod(trans(matrix), rhs_trans);

viennacl::vector<ScalarType> vcl_rhs_trans(rhs_trans.size());
viennacl::vector<ScalarType> vcl_result_trans(result_trans.size());
viennacl::copy(rhs_trans.begin(), rhs_trans.end(), vcl_rhs_trans.begin());
vcl_result_trans = viennacl::linalg::prod(trans(vcl_matrix), vcl_rhs_trans);

Direct Solver

In order to demonstrate the direct solvers, we first need to setup suitable square matrices. This is again achieved by running the setup on the CPU and then copy the data over to ViennaCL types:

ublas::matrix<ScalarType> tri_matrix(10,10);
for (std::size_t i=0; i<tri_matrix.size1(); ++i)
{
  for (std::size_t j=0; j<i; ++j)
    tri_matrix(i,j) = 0.0;

  for (std::size_t j=i; j<tri_matrix.size2(); ++j)
    tri_matrix(i,j) = matrix(i,j);
}

viennacl::matrix<ScalarType> vcl_tri_matrix = viennacl::identity_matrix<ScalarType>(tri_matrix.size1());
viennacl::copy(tri_matrix, vcl_tri_matrix);

// Bring vectors to correct size:
rhs.resize(tri_matrix.size1(), true);
rhs2.resize(tri_matrix.size1(), true);
vcl_rhs.resize(tri_matrix.size1(), true);

viennacl::copy(rhs.begin(), rhs.end(), vcl_rhs.begin());
vcl_result.resize(10);

Run a triangular solver on the upper triangular part of the matrix:

std::cout << "----- Upper Triangular solve -----" << std::endl;
result = ublas::solve(tri_matrix, rhs, ublas::upper_tag());                                    //ublas
vcl_result = viennacl::linalg::solve(vcl_tri_matrix, vcl_rhs, viennacl::linalg::upper_tag());  //ViennaCL

Inplace variants of triangular solvers:

ublas::inplace_solve(tri_matrix, rhs, ublas::upper_tag());                                //ublas
viennacl::linalg::inplace_solve(vcl_tri_matrix, vcl_rhs, viennacl::linalg::upper_tag());  //ViennaCL

Set up a full system for full solver using LU factorizations:

std::cout << "----- LU factorization -----" << std::endl;
std::size_t lu_dim = 300;
ublas::matrix<ScalarType> square_matrix(lu_dim, lu_dim);
ublas::vector<ScalarType> lu_rhs(lu_dim);
viennacl::matrix<ScalarType> vcl_square_matrix(lu_dim, lu_dim);
viennacl::vector<ScalarType> vcl_lu_rhs(lu_dim);

for (std::size_t i=0; i<lu_dim; ++i)
  for (std::size_t j=0; j<lu_dim; ++j)
    square_matrix(i,j) = randomNumber();

//put some more weight on diagonal elements:
for (std::size_t j=0; j<lu_dim; ++j)
{
  square_matrix(j,j) += ScalarType(10.0);
  lu_rhs(j) = randomNumber();
}

viennacl::copy(square_matrix, vcl_square_matrix);
viennacl::copy(lu_rhs, vcl_lu_rhs);
viennacl::linalg::lu_factorize(vcl_square_matrix);
viennacl::linalg::lu_substitute(vcl_square_matrix, vcl_lu_rhs);
viennacl::copy(square_matrix, vcl_square_matrix);
viennacl::copy(lu_rhs, vcl_lu_rhs);

Full solver with Boost.uBLAS:

ublas::lu_factorize(square_matrix);
ublas::inplace_solve (square_matrix, lu_rhs, ublas::unit_lower_tag ());
ublas::inplace_solve (square_matrix, lu_rhs, ublas::upper_tag ());

Full solver with ViennaCL:

viennacl::linalg::lu_factorize(vcl_square_matrix);
viennacl::linalg::lu_substitute(vcl_square_matrix, vcl_lu_rhs);

That's it.

  std::cout << "!!!! TUTORIAL COMPLETED SUCCESSFULLY !!!!" << std::endl;

  return EXIT_SUCCESS;
}

Full Example Code

/* =========================================================================
   Copyright (c) 2010-2016, Institute for Microelectronics,
                            Institute for Analysis and Scientific Computing,
                            TU Wien.
   Portions of this software are copyright by UChicago Argonne, LLC.

                            -----------------
                  ViennaCL - The Vienna Computing Library
                            -----------------

   Project Head:    Karl Rupp                   rupp@iue.tuwien.ac.at

   (A list of authors and contributors can be found in the PDF manual)

   License:         MIT (X11), see file LICENSE in the base directory
============================================================================= */

// System headers
#include <iostream>

// uBLAS headers
#include <boost/numeric/ublas/io.hpp>
#include <boost/numeric/ublas/triangular.hpp>
#include <boost/numeric/ublas/matrix_sparse.hpp>
#include <boost/numeric/ublas/matrix.hpp>
#include <boost/numeric/ublas/matrix_proxy.hpp>
#include <boost/numeric/ublas/vector_proxy.hpp>
#include <boost/numeric/ublas/lu.hpp>
#include <boost/numeric/ublas/io.hpp>


// Must be set if you want to use ViennaCL algorithms on ublas objects
#define VIENNACL_WITH_UBLAS 1

// ViennaCL headers
#include "viennacl/scalar.hpp"
#include "viennacl/vector.hpp"
#include "viennacl/matrix.hpp"
#include "viennacl/linalg/direct_solve.hpp"
#include "viennacl/linalg/prod.hpp"       //generic matrix-vector product
#include "viennacl/linalg/norm_2.hpp"     //generic l2-norm for vectors
#include "viennacl/linalg/lu.hpp"         //LU substitution routines
#include "viennacl/tools/random.hpp"

// Make `boost::numeric::ublas` available under the shortcut `ublas`:
using namespace boost::numeric;

int main()
{
  typedef float       ScalarType;

  viennacl::tools::uniform_random_numbers<ScalarType> randomNumber;

  ublas::vector<ScalarType> rhs(12);
  for (unsigned int i = 0; i < rhs.size(); ++i)
    rhs(i) = randomNumber();
  ublas::vector<ScalarType> rhs2 = rhs;
  ublas::vector<ScalarType> result = ublas::zero_vector<ScalarType>(10);
  ublas::vector<ScalarType> result2 = result;
  ublas::vector<ScalarType> rhs_trans = rhs;
  rhs_trans.resize(result.size(), true);
  ublas::vector<ScalarType> result_trans = ublas::zero_vector<ScalarType>(rhs.size());

  ublas::matrix<ScalarType> matrix(result.size(),rhs.size());

  for (unsigned int i = 0; i < matrix.size1(); ++i)
    for (unsigned int j = 0; j < matrix.size2(); ++j)
      matrix(i,j) = randomNumber();

  std::vector< ScalarType > stl_result(result.size());
  std::vector< ScalarType > stl_rhs(rhs.size());
  std::vector< std::vector<ScalarType> > stl_matrix(result.size());
  for (unsigned int i=0; i < result.size(); ++i)
  {
    stl_matrix[i].resize(rhs.size());
    for (unsigned int j = 0; j < matrix.size2(); ++j)
    {
      stl_rhs[j] = rhs[j];
      stl_matrix[i][j] = matrix(i,j);
    }
  }

  viennacl::vector<ScalarType> vcl_rhs(rhs.size());
  viennacl::vector<ScalarType> vcl_result(result.size());
  viennacl::matrix<ScalarType> vcl_matrix(result.size(), rhs.size());
  viennacl::matrix<ScalarType> vcl_matrix2(result.size(), rhs.size());

  viennacl::copy(rhs.begin(), rhs.end(), vcl_rhs.begin());
  viennacl::copy(matrix, vcl_matrix);     //copy from ublas dense matrix type to ViennaCL type

  vcl_matrix2 = vcl_matrix;
  vcl_matrix2 += vcl_matrix;
  vcl_matrix2 -= vcl_matrix;
  vcl_matrix2 = vcl_matrix2 + vcl_matrix;
  vcl_matrix2 = vcl_matrix2 - vcl_matrix;

  viennacl::scalar<ScalarType> vcl_3(3.0);
  vcl_matrix2 *= ScalarType(2.0);
  vcl_matrix2 /= ScalarType(2.0);
  vcl_matrix2 *= vcl_3;
  vcl_matrix2 /= vcl_3;

  vcl_matrix.clear();

  viennacl::copy(stl_matrix, vcl_matrix); //alternative: copy from STL vector< vector<> > type to ViennaCL type

  //for demonstration purposes (no effect):
  viennacl::copy(vcl_matrix, matrix); //copy back from ViennaCL to ublas type.
  viennacl::copy(vcl_matrix, stl_matrix); //copy back from ViennaCL to STL type.

  std::cout << "----- Matrix-Vector product -----" << std::endl;
  result = ublas::prod(matrix, rhs);                            //the ublas way
  stl_result = viennacl::linalg::prod(stl_matrix, stl_rhs);     //using STL
  vcl_result = viennacl::linalg::prod(vcl_matrix, vcl_rhs);     //the ViennaCL way

  std::cout << "----- Transposed Matrix-Vector product -----" << std::endl;
  result_trans = prod(trans(matrix), rhs_trans);

  viennacl::vector<ScalarType> vcl_rhs_trans(rhs_trans.size());
  viennacl::vector<ScalarType> vcl_result_trans(result_trans.size());
  viennacl::copy(rhs_trans.begin(), rhs_trans.end(), vcl_rhs_trans.begin());
  vcl_result_trans = viennacl::linalg::prod(trans(vcl_matrix), vcl_rhs_trans);



  ublas::matrix<ScalarType> tri_matrix(10,10);
  for (std::size_t i=0; i<tri_matrix.size1(); ++i)
  {
    for (std::size_t j=0; j<i; ++j)
      tri_matrix(i,j) = 0.0;

    for (std::size_t j=i; j<tri_matrix.size2(); ++j)
      tri_matrix(i,j) = matrix(i,j);
  }

  viennacl::matrix<ScalarType> vcl_tri_matrix = viennacl::identity_matrix<ScalarType>(tri_matrix.size1());
  viennacl::copy(tri_matrix, vcl_tri_matrix);

  // Bring vectors to correct size:
  rhs.resize(tri_matrix.size1(), true);
  rhs2.resize(tri_matrix.size1(), true);
  vcl_rhs.resize(tri_matrix.size1(), true);

  viennacl::copy(rhs.begin(), rhs.end(), vcl_rhs.begin());
  vcl_result.resize(10);


  std::cout << "----- Upper Triangular solve -----" << std::endl;
  result = ublas::solve(tri_matrix, rhs, ublas::upper_tag());                                    //ublas
  vcl_result = viennacl::linalg::solve(vcl_tri_matrix, vcl_rhs, viennacl::linalg::upper_tag());  //ViennaCL

  ublas::inplace_solve(tri_matrix, rhs, ublas::upper_tag());                                //ublas
  viennacl::linalg::inplace_solve(vcl_tri_matrix, vcl_rhs, viennacl::linalg::upper_tag());  //ViennaCL


  std::cout << "----- LU factorization -----" << std::endl;
  std::size_t lu_dim = 300;
  ublas::matrix<ScalarType> square_matrix(lu_dim, lu_dim);
  ublas::vector<ScalarType> lu_rhs(lu_dim);
  viennacl::matrix<ScalarType> vcl_square_matrix(lu_dim, lu_dim);
  viennacl::vector<ScalarType> vcl_lu_rhs(lu_dim);

  for (std::size_t i=0; i<lu_dim; ++i)
    for (std::size_t j=0; j<lu_dim; ++j)
      square_matrix(i,j) = randomNumber();

  //put some more weight on diagonal elements:
  for (std::size_t j=0; j<lu_dim; ++j)
  {
    square_matrix(j,j) += ScalarType(10.0);
    lu_rhs(j) = randomNumber();
  }

  viennacl::copy(square_matrix, vcl_square_matrix);
  viennacl::copy(lu_rhs, vcl_lu_rhs);
  viennacl::linalg::lu_factorize(vcl_square_matrix);
  viennacl::linalg::lu_substitute(vcl_square_matrix, vcl_lu_rhs);
  viennacl::copy(square_matrix, vcl_square_matrix);
  viennacl::copy(lu_rhs, vcl_lu_rhs);


  ublas::lu_factorize(square_matrix);
  ublas::inplace_solve (square_matrix, lu_rhs, ublas::unit_lower_tag ());
  ublas::inplace_solve (square_matrix, lu_rhs, ublas::upper_tag ());


  viennacl::linalg::lu_factorize(vcl_square_matrix);
  viennacl::linalg::lu_substitute(vcl_square_matrix, vcl_lu_rhs);

  std::cout << "!!!! TUTORIAL COMPLETED SUCCESSFULLY !!!!" << std::endl;

  return EXIT_SUCCESS;
}