Fixed asserts in the diagonal preconditioner for empty matrices

Diagonal< Matrices::DistributedMatrix< Matrix > >::

update( const MatrixPointer& matrixPointer )

{

   TNL_ASSERT_GT( matrixPointer->getRows(), 0, "empty matrix" );

   diagonal.setSize( matrixPointer->getLocalMatrix().getRows() );

   LocalViewType diag_view( diagonal );

   }

   else {

      // non-square matrix, assume ghost indexing

      TNL_ASSERT_LT( matrixPointer->getLocalMatrix().getRows(), matrixPointer->getLocalMatrix().getColumns(), "the local matrix should have more columns than rows" );

      TNL_ASSERT_LE( matrixPointer->getLocalMatrix().getRows(), matrixPointer->getLocalMatrix().getColumns(), "the local matrix should have more columns than rows" );

      auto kernel = [=] __cuda_callable__ ( IndexType i ) mutable

      {

         diag_view[ i ] = matrix_view.getElement( i, i );