[ublas] FE assembly : a huge time time difference

Subject: [ublas] FE assembly : a huge time time difference
From: Umut Tabak (u.tabak_at_[hidden])
Date: 2010-12-29 20:15:57

Dear all,

I was trying to read some system matrices from the commercial code ANSYS 
to boost compressed_matrices (I saw the links of Gunther Winkler however 
did not have the time to try yet), but the question is what is the 
fastest way to assemble in FE sense,

In pseudo code notation, ke is the element matrix

K(dofs, dofs) = K(dofs, dofs) + ke

So some technical detail that might help, ANSYS stores the symmetric 
element matrices such as the ones result from structural elements in 
lower triangular format

I did some coding like below, as a first try however seems slow, and 
thought that there should be a faster way to do this.

Should I use indirect_array to assign the submatrices of element 
contributions or what should be the right way to do this?

Any pointers are appreciated.

Best wishes,
Umut

    unsigned r=0, sI = 0; // row, and startIndex
                          // for the lower triangular format
    // read the dofs to assign
    //dofIndxTable : dofs vector
    // vals the lower triangular matrix in col oriented order
    // reason why I use the slices here
    for( std::vector<int>::const_iterator rowIter = dofIndxTable.begin();
         rowIter != dofIndxTable.end(); ++rowIter 
){                                                                                         

        vector_slice<vector <double> > vs( valsK, slice( sI, 1, r+1) );
        unsigned clSz = vs.size();
        unsigned c = 0;
        for( std::vector<int>::const_iterator colIter = 
dofIndxTable.begin();
       (colIter != dofIndxTable.end() & c!=clSz); ++colIter ){
          if ( r == c)
              K( *rowIter-1, *colIter-1 ) += vs(c);
          else{ 
              K( *rowIter-1, *colIter-1 ) += vs(c);
              K( *colIter-1, *rowIter-1 ) += vs(c);
          }     
          ++c;  
        }     
        sI += vs.size();
        ++r;  
    }