containers/benchmark_naive_matrix.cpp

This is an example of how to represent a 2D matrix by using an stxxl::vector. DISCLAIMER: The approach is very basic and the matrix multiplication is NOT I/O-EFFICIENT.

/***************************************************************************
 * containers/benchmark_naive_matrix.cpp
 *
 * Part of the STXXL. See http://stxxl.sourceforge.net
 *
 * Copyright (C) 2010 Johannes Singler <[email protected]>
 *
 * 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)
 **************************************************************************/


#include <iostream>
#include <stxxl/vector>

template <typename T>
class matrix2d
{
 stxxl::vector<T> v;
 stxxl::unsigned_type width, height;

public:
 matrix2d(stxxl::unsigned_type width, stxxl::unsigned_type height) : width(width), height(height)
 {
 v.resize(width * height);
 }

 stxxl::unsigned_type get_width() const
 {
 return width;
 }

 stxxl::unsigned_type get_height() const
 {
 return height;
 }


 T & element(stxxl::unsigned_type x, stxxl::unsigned_type y)
 {
 //row-major
 return v[y * width + x];
 }

 const T & const_element(stxxl::unsigned_type x, stxxl::unsigned_type y) const
 {
 //row-major
 return v[y * width + x];
 }
};

template <typename T>
void matrix_multiply(const matrix2d<T> & a, const matrix2d<T> & b, matrix2d<T> & c)
{
 assert(a.get_width() == b.get_height());
 assert(b.get_height() == c.get_height());
 assert(b.get_width() == c.get_width());

 for (stxxl::unsigned_type y = 0; y < c.get_height(); ++y)
 for (stxxl::unsigned_type x = 0; x < c.get_width(); ++x)
 {
 c.element(x, y) = 0;
 for (stxxl::unsigned_type t = 0; t < a.get_width(); ++t)
 c.element(x, y) += a.const_element(t, y) * b.const_element(x, t);
 }
}

int main()
{
 const stxxl::unsigned_type width = 416, height = 416;

 try
 {
 matrix2d<double> a(width, height), b(width, height), c(width, height);

 for (stxxl::unsigned_type y = 0; y < height; ++y)
 for (stxxl::unsigned_type x = 0; x < width; ++x)
 {
 a.element(x, y) = 1.0;
 b.element(x, y) = 1.0;
 c.element(x, y) = 1.0;
 }

 matrix_multiply(a, b, c);

 std::cout << c.const_element(0, 0) << std::endl;
 std::cout << c.const_element(width - 1, height - 1) << std::endl;
 }
 catch (const std::exception & ex)
 {
 STXXL_MSG("Caught exception: " << ex.what());
 }
 catch (...)
 {
 STXXL_MSG("Caught unknown exception.");
 }

 return 0;
}