[Octave-bug-tracker] [bug #51880] sparse() ignores value of scalar column index input arg

[Rik]

Update of bug #51880 (project octave):

                  Status:          Ready For Test => Fixed                  
             Open/Closed:                    Open => Closed                 

    _______________________________________________________

Follow-up Comment #8:

Only way to know was to benchmark it.  Indeed, the resizing of the SparseRep
was not a driver of execution time.  However, I did find that using
std::fill_n over only the non-zero columns provided ~20% savings.

The benchmark code was


N = 1e3;

bm = zeros (N, 1);
for i = 1:N
  clear x;
  tic;
  x = sparse (1:2:2000, 9999, 1:1000, 1e4, 1e4);
  bm(i) = toc;
  pause (.010);
endfor


By putting everything in the next to last column this was clearly worst case,
but it did beat the handcoded for loop.  Replacement code was


-          xcidx (0) = 0;
-          for (octave_idx_type j = 0; j < nc; j++)
-            xcidx (j+1) = j >= c(0) ? new_nz : 0;
+          std::fill_n (xcidx () + c(0) + 1, nc - c(0), new_nz);


I checked in the full cset here
(http://hg.savannah.gnu.org/hgweb/octave/rev/584971932def).


    _______________________________________________________

Reply to this item at:

  <http://savannah.gnu.org/bugs/?51880>

_______________________________________________
  Message sent via/by Savannah
  http://savannah.gnu.org/