1 files changed, 110 insertions, 0 deletions
diff --git a/methods/powell/brent.hpp b/methods/powell/brent.hpp
new file mode 100644
index 0000000..cb3b962
--- /dev/null
+++ b/methods/powell/brent.hpp
@@ -0,0 +1,110 @@
+#ifndef BRENT_HPP
+#define BRENT_HPP
+#include <iostream>
+#include "bas_util.hpp"
+//#include "optimizer.hpp"
+namespace opt_utilities
+{
+  template<typename T>
+  T brent(T ax,T bx,T cx,func_obj<T,T>& f,T tol,T& xmin)
+  {
+    const int ITMAX=100;
+    const T CGOLD=0.3819660;
+    const T ZEPS=std::numeric_limits<T>::epsilon()*1.e-3;
+    
+    int iter;
+    T a=0,b=0,d(0),etemp=0,fu=0,fv=0,fw=0,fx=0,p=0,q=0
+      ,r=0,tol1=0,tol2=0,u=0,v=0,w=0,x=0,xm=0;
+    T e=0.;
+    a=(ax<cx?ax:cx);
+    b=(ax>cx?ax:cx);
+    x=w=v=bx;
+    fw=fv=fx=f.eval(x);
+    for(iter=0;iter<ITMAX;++iter)
+      {
+	xm=.5*(a+b);
+	tol2=2.*(tol1=tol*tabs(x)+ZEPS);
+	if(tabs(T(x-xm))<=(tol2-.5*(b-a)))
+	  {
+	    xmin=x;
+	    return fx;
+	  }
+	if(tabs(e)>tol1)
+	  {
+	    r=(x-w)*(fx-fv);
+	    q=(x-v)*(fx-fw);
+	    p=(x-v)*q-(x-w)*r;
+	    q=2.*(q-r);
+	    if(q>0.)
+	      {
+		p=-p;
+	      }
+	    q=tabs(q);
+	    etemp=e;
+	    e=d;
+	    if(tabs(p)>=tabs(T(T(.5)*p*etemp))||p<=q*(a-x)||p>=q*(b-x))
+	      {
+		d=CGOLD*(e=(x>=xm?a-x:b-x));
+	      }
+	    else
+	      {
+		d=p/q;
+		u=x+d;
+		if(u-a<tol2||b-u<tol2)
+		  {
+		    d=sign(tol1,T(xm-x));
+		  }
+	      }
+	    
+	  }
+	else
+	  {
+	    d=CGOLD*(e=(x>=xm?a-x:b-x));
+	  }
+	u=(tabs(d)>=tol1?x+d:x+sign(tol1,d));
+	fu=f.eval(u);
+	if(fu<=fx)
+	  {
+	    if(u>=x)
+	      {
+		a=x;
+	      }
+	    else
+	      {
+		b=x;
+	      }
+	    shft3(v,w,x,u);
+	    shft3(fv,fw,fx,fu);
+	  }
+	else
+	  {
+	    if(u<x)
+	      {
+		a=u;
+	      }
+	    else
+	      {
+		b=u;
+	      }
+	    if(fu<=fw||w==x)
+	      {
+		v=w;
+		w=u;
+		fv=fw;
+		fw=fu;
+	      }
+	    else if(fu<=fv||v==x||v==w)
+	      {
+		v=u;
+		fv=fu;
+	      }
+	  }
+      }
+    std::cerr<<"Too many iterations in brent"<<std::endl;
+    xmin=x;
+    return fx;
+    
+  }
+}
+
+#endif