/*
    Fmin.java copyright claim:

    This software is based on the public domain fmin routine.
    The FORTRAN version can be found at

    www.netlib.org

    This software was translated from the FORTRAN version
    to Java by a US government employee on official time.  
    Thus this software is also in the public domain.


    The translator's mail address is:

    Steve Verrill 
    USDA Forest Products Laboratory
    1 Gifford Pinchot Drive
    Madison, Wisconsin
    53705


    The translator's e-mail address is:

    steve@www1.fpl.fs.fed.us


***********************************************************************

DISCLAIMER OF WARRANTIES:

THIS SOFTWARE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. 
THE TRANSLATOR DOES NOT WARRANT, GUARANTEE OR MAKE ANY REPRESENTATIONS 
REGARDING THE SOFTWARE OR DOCUMENTATION IN TERMS OF THEIR CORRECTNESS, 
RELIABILITY, CURRENTNESS, OR OTHERWISE. THE ENTIRE RISK AS TO 
THE RESULTS AND PERFORMANCE OF THE SOFTWARE IS ASSUMED BY YOU. 
IN NO CASE WILL ANY PARTY INVOLVED WITH THE CREATION OR DISTRIBUTION 
OF THE SOFTWARE BE LIABLE FOR ANY DAMAGE THAT MAY RESULT FROM THE USE 
OF THIS SOFTWARE.

Sorry about that.

***********************************************************************


History:

Date        Translator        Changes

3/24/98     Steve Verrill     Translated
2/11/06     Jonas Forssell    Adopted to suit Impact

*/


package util;


/**
*
*<p>
*This class was translated by a statistician from the FORTRAN 
*version of fmin.  It is NOT an official translation.  When 
*public domain Java optimization routines become available 
*from professional numerical analysts, then <b>THE CODE PRODUCED
*BY THE NUMERICAL ANALYSTS SHOULD BE USED</b>.
*
*<p>
*Meanwhile, if you have suggestions for improving this
*code, please contact Steve Verrill at steve@www1.fpl.fs.fed.us.
*
*@author Steve Verrill
*@version .5 --- March 24, 1998
* 
*/

public class GoldenSection extends Object {

/**
*
*<p>
*This method performs a 1-dimensional minimization.
*It implements Brent's method which combines a golden-section
*search and parabolic interpolation.  The introductory comments from
*the FORTRAN version are provided below.
*
*This method is a translation from FORTRAN to Java of the Netlib 
*function fmin.  In the Netlib listing no author is given.
*
*Translated by Steve Verrill, March 24, 1998.
*
*@param  a         Left endpoint of initial interval
*@param  b         Right endpoint of initial interval
*@param  minclass  A class that defines a method, f_to_minimize,
*                  to minimize.  The class must implement
*                  the Fmin_methods interface (see the definition
*                  in Fmin_methods.java).  See FminTest.java
*                  for an example of such a class.
*                  f_to_minimize must have one
*                  double valued argument.
*@param  tol       Desired length of the interval in which
*                  the minimum will be determined to lie
*                  (This should be greater than, roughly, 3.0e-8.)
*
*/


   public static double minimize (double a, double b, SingleFunction minclass,
                              double tol) {

/*

Here is a copy of the Netlib documentation:

c
c      An approximation x to the point where f attains a minimum on
c  the interval (ax,bx) is determined.
c
c  input..
c
c  ax    left endpoint of initial interval
c  bx    right endpoint of initial interval
c  f     function subprogram which evaluates f(x) for any x
c        in the interval (ax,bx)
c  tol   desired length of the interval of uncertainty of the final
c        result (.ge.0.)
c
c  output..
c
c  fmin  abcissa approximating the point where  f  attains a
c        minimum
c
c     The method used is a combination of golden section search and
c  successive parabolic interpolation.  Convergence is never much slower
c  than that for a Fibonacci search.  If f has a continuous second
c  derivative which is positive at the minimum (which is not at ax or
c  bx), then convergence is superlinear, and usually of the order of
c  about 1.324.
c     The function f is never evaluated at two points closer together
c  than eps*abs(fmin)+(tol/3), where eps is approximately the square
c  root of the relative machine precision.  If f is a unimodal
c  function and the computed values of f are always unimodal when
c  separated by at least eps*abs(x)+(tol/3), then fmin approximates
c  the abcissa of the global minimum of f on the interval (ax,bx) with
c  an error less than 3*eps*abs(fmin)+tol.  If f is not unimodal,
c  then fmin may approximate a local, but perhaps non-global, minimum to
c  the same accuracy.
c      This function subprogram is a slightly modified version of the
c  Algol 60 procedure localmin given in Richard Brent, Algorithms For
c  Minimization Without Derivatives, Prentice-Hall, Inc. (1973).
c

*/

      double c,d,e,eps,xm,p,q,r,tol1,t2,
             u,v,w,fu,fv,fw,fx,x,tol3;

      c = .5*(3.0 - Math.sqrt(5.0));
      d = 0.0;

// 1.1102e-16 is machine precision

      eps = 1.2e-16;
      tol1 = eps + 1.0;
      eps = Math.sqrt(eps);

      v = a + c*(b-a);
      w = v;
      x = v;
      e = 0.0;
      fx = minclass.f(x);
      fv = fx;
      fw = fx;
      tol3 = tol/3.0;

      xm = .5*(a + b);
      tol1 = eps*Math.abs(x) + tol3;
      t2 = 2.0*tol1;

// main loop

      while (Math.abs(x-xm) > (t2 - .5*(b-a))) {

         p = q = r = 0.0;

         if (Math.abs(e) > tol1) {

// fit the parabola

            r = (x-w)*(fx-fv);
            q = (x-v)*(fx-fw);
            p = (x-v)*q - (x-w)*r;
            q = 2.0*(q-r);

            if (q > 0.0) {

               p = -p;

            } else {

               q = -q;

            }

            r = e;
            e = d;         

// brace below corresponds to statement 50
         }

         if ((Math.abs(p) < Math.abs(.5*q*r)) &&
             (p > q*(a-x)) &&
             (p < q*(b-x))) {

// a parabolic interpolation step

            d = p/q;
            u = x+d;

// f must not be evaluated too close to a or b

            if (((u-a) < t2) || ((b-u) < t2)) {

               d = tol1;
               if (x >= xm) d = -d;

            }

// brace below corresponds to statement 60
         } else {

// a golden-section step

            if (x < xm) {

               e = b-x;

            } else {

               e = a-x;

            }

            d = c*e;

         }

// f must not be evaluated too close to x

         if (Math.abs(d) >= tol1) {

            u = x+d;

         } else {

            if (d > 0.0) {

               u = x + tol1;

            } else {

               u = x - tol1;

            }

         }

         fu = minclass.f(u);

// Update a, b, v, w, and x

         if (fx <= fu) {

            if (u < x) {

               a = u;

            } else {

               b = u;

            }

// brace below corresponds to statement 140
         }

         if (fu <= fx) {

            if (u < x) {

               b = x;

            } else {

               a = x;

            }

            v = w;
            fv = fw;
            w = x;
            fw = fx;
            x = u;
            fx = fu;

            xm = .5*(a + b);
            tol1 = eps*Math.abs(x) + tol3;
            t2 = 2.0*tol1;

// brace below corresponds to statement 170
         } else {

            if ((fu <= fw) || (w == x)) {

               v = w;
               fv = fw;
               w = u;
               fw = fu;

               xm = .5*(a + b);
               tol1 = eps*Math.abs(x) + tol3;
               t2 = 2.0*tol1;

            } else if ((fu > fv) && (v != x) && (v != w)) {

               xm = .5*(a + b);
               tol1 = eps*Math.abs(x) + tol3;
               t2 = 2.0*tol1;

            } else {

               v = u;
               fv = fu;

               xm = .5*(a + b);
               tol1 = eps*Math.abs(x) + tol3;
               t2 = 2.0*tol1;

            }

         }

// brace below corresponds to statement 190
      }

      return x;

   }   
                                    
}
