From: Michael Orlitzky <michael@orlitzky.com>
Date: Sat, 23 Mar 2013 02:30:00 +0000 (-0400)
Subject: Avoid divide-by-zero in step_length_positive_definite.m.
X-Git-Url: https://gitweb.michael.orlitzky.com/?a=commitdiff_plain;h=99b1398f7acd8c15e42160c047dcaff816643020;p=octave.git

Avoid divide-by-zero in step_length_positive_definite.m.
---

diff --git a/optimization/step_length_positive_definite.m b/optimization/step_length_positive_definite.m
index ad63956..ced5562 100644
--- a/optimization/step_length_positive_definite.m
+++ b/optimization/step_length_positive_definite.m
@@ -32,5 +32,13 @@ function alpha = step_length_positive_definite(g, Q, p)
   %
   % All vectors are assumed to be *column* vectors.
   %
-  alpha = -(g' * p)/(p' * Q * p);
+  denom = (p' * Q * p);
+
+  if (abs(denom) > eps)
+    % Catch divide-by-zeros. If denom is effectively zero, set it to
+    % something tiny instead. This trick is also used in the PCGM.
+    denom = sign(denom)*eps;
+  end
+
+  alpha = -(g' * p)/denom;
 end