Join matrices and vectors

[Santiago Peñate Vera]

Hi,

I cannot find how to join several matrices or vectors into a new one.

My case is that I am programming a Newton-Raphson method and build the Jacobian, I need to create four sub-matrices (A, B, C, D) and then join them.

J = {{A, B}, {C, D}}

I also need to do this with vectors. Is this implemented?

[Klaus Iglberger]

Hi Santiago!

Thanks for creating this issue. Blaze does not provide the syntax you suggest to join matrices or vectors. One of the reasons is that the elements in an std::initializer_list are copy-initialized, which in this case would result in a significant and unacceptable overhead. Instead you should use Subvectors and Submatrices to assign to a specific part of a vector or matrix, respectively. For instance, the following join() function uses submatrices to assign A, B, C, and D to the four parts of the given matrix T:

template< typename MT1, bool SO1
        , typename MT2, bool SO2
        , typename MT3, bool SO3
        , typename MT4, bool SO4
        , typename MT5, bool SO5 > 
void join( const DenseMatrix<MT1,SO1>& A
         , const DenseMatrix<MT2,SO2>& B
         , const DenseMatrix<MT3,SO3>& C
         , const DenseMatrix<MT4,SO4>& D
         , DenseMatrix<MT5,SO5>& T )
{
   BLAZE_CONSTRAINT_MUST_BE_OPERATION_TYPE( MT5 );

   if( (~A).rows() != (~B).rows() ||
       (~C).rows() != (~D).rows() ||
       (~A).columns() != (~C).columns() ||
       (~B).columns() != (~D).columns() )
      throw std::invalid_argument( "Invalid matrix parameters for join operation" );

   const size_t M1( (~A).rows() );
   const size_t M2( (~C).rows() );
   const size_t N1( (~A).columns() );
   const size_t N2( (~B).columns() );

   resize( ~T, M1+M2, N1+N2 );

   submatrix( ~T, 0UL, 0UL, M1, N1 ) = A;
   submatrix( ~T, 0UL,  N1, M1, N2 ) = B;
   submatrix( ~T,  M1, 0UL, M2, N1 ) = C;
   submatrix( ~T,  M1,  N1, M2, N2 ) = D;
}

An alternative approach will be the block matrix view, which has been requested in issue #149. Please feel free to vote for this issue and to watch it if you are interested in the progress. Thanks again for creating this issue,

Best regards,

Klaus!

[Klaus Iglberger]

Duplicate of #149.