# HG changeset patch
# User Jaroslav Hajek <highegg@gmail.com>
# Date 1252651645 -7200
# Node ID ecc2c556f844b30734ac42e2474e90d593197bcf
# Parent  40acd13920e36f2e0ac9318cf9f96017ecd8a515
simplify damped BFGS formula

diff --git a/scripts/ChangeLog b/scripts/ChangeLog
--- a/scripts/ChangeLog
+++ b/scripts/ChangeLog
@@ -1,3 +1,7 @@
+2009-09-11  Jaroslav Hajek  <highegg@gmail.com>
+
+	* optimization/fminunc.m: Simplify damped BFGS calculation.
+
 2009-09-09  Tatsuro Matsuoka <tmacchant@yahoo.co.jp>
 
 	* plot/gnuplot_drawnow.m: Avoid flickering windows by avoding
diff --git a/scripts/optimization/fminunc.m b/scripts/optimization/fminunc.m
--- a/scripts/optimization/fminunc.m
+++ b/scripts/optimization/fminunc.m
@@ -170,11 +170,7 @@
       sBs = sumsq (w);
       Bs = hesr'*w;
       sy = y'*s;
-      if (sy >= 0.2*sBs)
-        theta = 1;
-      else
-        theta = 0.8*sBs / (sBs - sy);
-      endif
+      theta = 0.8 / max (1 - sy / sBs, 0.8);
       r = theta * y + (1-theta) * Bs;
       hesr = cholupdate (hesr, r / sqrt (s'*r), "+");
       [hesr, info] = cholupdate (hesr, Bs / sqrt (sBs), "-");