Limit the number of iterations in bracketing mode to 4.

This is necessary to avoid situations where the algorithm remains
stuck in bracketing mode due to an inaccurated derivative at the
end point.


git-svn-id: http://qboxcode.org/svn/qb/trunk@912 cba15fb0-1239-40c8-b417-11db7ca47a34

src/LineMinimizer.h

@@ -15,7 +15,6 @@
 // LineMinimizer.h
 //
 ////////////////////////////////////////////////////////////////////////////////
-// $Id: LineMinimizer.h,v 1.3 2008-09-08 15:56:18 fgygi Exp $
 
 #ifndef LINEMINIMIZER_H
 #define LINEMINIMIZER_H
@@ -33,6 +32,10 @@ class LineMinimizer
   double f_low, fp_low, f_high, fp_high;
   double f0, fp0;
   bool bracket, first_use;
+  // number of iterations in bracketing mode
+  int nbracket;
+  // maximum number of iterations in bracketing mode
+  enum { nbracket_max = 4 };
   bool debug_print;
   double interpolate(void)
   {
@@ -68,8 +71,8 @@ class LineMinimizer
   public:
 
   LineMinimizer(void) : sigma1_(0.1), alpha_start(1.0), first_use(true),
-   debug_print(false) {}
-  void reset(void) { first_use = true; }
+   debug_print(false), nbracket(0) {}
+  void reset(void) { first_use = true; nbracket = 0; }
   double sigma1(void) const { return sigma1_; }
   void set_sigma1(double s1) { sigma1_ = s1; }
   double newalpha(double alpha, double f, double fp)
@@ -134,6 +137,10 @@ class LineMinimizer
     else
     {
       // we are in the bracketing phase
+      // check how many iterations have been done so far in bracketing mode
+      // and reset if more than 3
+      if ( nbracket++ > 3)
+        reset();
       if ( debug_print )
       {
         std::cout << " LineMinimizer: bracketing, alpha_low/high = "