Example: math_csparse_example

C++ example source code:

/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2025, Individual contributors, see AUTHORS file     |
   | See: https://www.mrpt.org/Authors - All rights reserved.               |
   | Released under BSD License. See: https://www.mrpt.org/License          |
   +------------------------------------------------------------------------+ */

#include <mrpt/math/CSparseMatrix.h>
#include <mrpt/random/RandomGenerators.h>

#include <iostream>

using namespace mrpt;
using namespace mrpt::math;
using namespace std;

void ExampleCSparse()
{
  // Initialize a 10x10 sparse matrix:
  CSparseMatrix SM(10, 10);

  // With 2 dense blocks of 6x6 and 4x4:
  const auto COV1 =
      mrpt::random::getRandomGenerator().drawDefinitePositiveMatrix<CMatrixDouble>(6, 0.2);
  const auto COV2 =
      mrpt::random::getRandomGenerator().drawDefinitePositiveMatrix<CMatrixDouble>(4, 0.2);
  SM.insert_submatrix(0, 0, COV1);
  SM.insert_submatrix(6, 6, COV2);

  // Get as a dense matrix just for displaying to console:
  CMatrixDouble M;
  SM.get_dense(M);
  cout << "M (as dense):\n" << M;

  cout << "Saving to sparse_demo1.txt...\n";
  bool savedOk = SM.saveToTextFile_sparse("sparse_demo1.txt");
  ASSERT_(savedOk);

  // Compress from the triplet to the column-compressed form:
  cout << "Compressing as CCS...\n";
  SM.compressFromTriplet();

  cout << "Saving to sparse_demo2.txt...\n";
  savedOk = SM.saveToTextFile_sparse("sparse_demo2.txt");
  ASSERT_(savedOk);

  // Compute the Cholesky decomposition:
  CSparseMatrix::CholeskyDecomp Chol(SM);

  // And display the L factor:
  const CMatrixDouble L = Chol.get_L();
  cout << "L:\n" << L << endl;
}

int main(int argc, char** argv)
{
  try
  {
    ExampleCSparse();
    return 0;
  }
  catch (exception& e)
  {
    cout << "MRPT exception caught: " << e.what() << endl;
    return -1;
  }
  catch (...)
  {
    printf("Another exception!!");
    return -1;
  }
}