<div dir="ltr"><div>Hi <span style="color:rgb(0,0,0);white-space:pre-wrap">Markus</span>,<br></div><div><br></div><div>thank you for the prompt reply, I was just thinking about some thing like matMultMat() in <dune/istl/matrixmatrix.hh>, example below,</div><div><br></div><div>example:</div><div><span class="Apple-tab-span" style="white-space:pre">       </span>    typedef Dune::BCRSMatrix<Dune::FieldMatrix<double,1,1> > ScalarMatrix;</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre">    </span>    ScalarMatrix A(2,2,ScalarMatrix::random);</div><div><span class="Apple-tab-span" style="white-space:pre">      </span>    A.setrowsize(0,1);</div><div><span class="Apple-tab-span" style="white-space:pre">     </span>    A.endrowsizes();</div><div><span class="Apple-tab-span" style="white-space:pre">       </span>    A.addindex(0,0);</div><div><span class="Apple-tab-span" style="white-space:pre">       </span>    A.endindices();</div><div><span class="Apple-tab-span" style="white-space:pre">        </span>    Dune::printmatrix(std::cout, A, "A", "row");</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre">      </span>    ScalarMatrix B(2,2,ScalarMatrix::random);</div><div><span class="Apple-tab-span" style="white-space:pre">      </span>    B.setrowsize(0,1);</div><div><span class="Apple-tab-span" style="white-space:pre">     </span>    B.endrowsizes();</div><div><span class="Apple-tab-span" style="white-space:pre">       </span>    B.addindex(0,1);</div><div><span class="Apple-tab-span" style="white-space:pre">       </span>    B.endindices();</div><div><span class="Apple-tab-span" style="white-space:pre">        </span>    Dune::printmatrix(std::cout, B, "B", "row");</div><div><br></div><div><span class="Apple-tab-span" style="white-space:pre">      </span>    ScalarMatrix C(2,2,ScalarMatrix::random);</div><div><span class="Apple-tab-span" style="white-space:pre">      </span>    // C = A * B;</div><div><span class="Apple-tab-span" style="white-space:pre">  </span>    matMultMat(C,A,B);</div><div><span class="Apple-tab-span" style="white-space:pre">     </span>    Dune::printmatrix(std::cout, C, "C", "row");</div><div><br></div><div>and the output,</div><div><br></div><div>A [n=2,m=2,rowdim=2,coldim=2]</div><div>row    0   0.00e+00          .</div><div>row    1          .          .</div><div>B [n=2,m=2,rowdim=2,coldim=2]</div><div>row    0          .   0.00e+00</div><div>row    1          .          .</div><div>C [n=2,m=2,rowdim=2,coldim=2]</div><div>row    0          .   0.00e+00</div><div>row    1          .          .</div><div><br></div><div>Adim</div></div>