tree 154303210de1c2d15832922d32d8ca34c902ae61
parent df0125666af1bf37878b8e5cab5c6479d1b90842
author Sameer Agarwal <sameeragarwal@google.com> 1369238886 -0700
committer Sameer Agarwal <sameeragarwal@google.com> 1369252738 -0700

Speed up corrector.cc

Remove the Eigen temporary by revealing the columnwise nature
of the computation. This also allows us to get rid of the
special case for nrow = 1.

On problem-356-226730-pre.txt with -robustify evaluation times
change from:

Before:
  Residual Evaluations                  1.015
  Jacobian Evaluations                 18.313

After:
  Residual Evaluations                  1.005
  Jacobian Evaluations                  8.382

To give a sense of the overhead reduction, compare these numbers
when loss functions are disabled.

  Residual Evaluations                  0.955
  Jacobian Evaluations                  7.772

So, this is a 17.5x speedup!

The one dimensional specialization was motivated by denoising.cc.
The evaluation times there are essentially unchanged.

Before:
  Residual Evaluations                  2.774
  Jacobian Evaluations                 20.178

After:
  Residual Evaluations                  2.588
  Jacobian Evaluations                 19.781

Change-Id: Ic0efbaed75fe4489635039f17189ae24b97802c8