tree 472f0742c346e3ea6286ef0d9d88a8af3d466043
parent a2e19f163a9e45ee4f768efcf2a7c7e1d10bdc0c
author Sameer Agarwal <sameeragarwal@google.com> 1422652328 -0800
committer Sameer Agarwal <sameeragarwal@google.com> 1422656405 -0800

Improve the error handling in Conjugte Gradients.

Due to floating point and conditioning issues, a system
matrix which is guaranteed to be PSD in exact arithmetic
can appear indefinite to the ConjugateGradientsSolver.

Previously, x'Ax <= 0, the solver returned with numerical
failure. Which the trust region solver will treat as a failed
solve.

But, more general truncated Newton when they encounter indefiniteness
use the step computed till that point instead of declaring failure.

This changes does this and adds a bit more logging.

Change-Id: I0e0cc56ef7d856f1c54ac6d638327b8353039f70