gssearch.m

这是在网上下的一个东东

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% [xmin,fxmin,newa,newb]=gssearch('f',a,u,b,tol)
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function [xmin,fxmin,newa,newb]=gssearch(fun,a,u,b,tol)
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%  Evaluate f at the end points of the interval, and initialize
%  xmin.
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newa=a;
fa=feval(fun,newa);
newb=b;
fb=feval(fun,newb);
if (fa < fb)
  xmin=newa;
  fxmin=fa;
else
  xmin=newb;
  fxmin=fb;
end

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% Calculate the locations of the two points inside the interval.
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u=newa+.3820*(newb-newa);
v=newa+0.6180*(newb-newa);

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%  Calculate f(u)
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fu=feval(fun,u);

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% Update xmin and fxmin.  
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if (fu < fxmin) 
  xmin=u;
  fxmin=fu;
end

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%  Calculate f(v)
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fv=feval(fun,v);

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%  Update fxmin and xmin.
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if (fv < fxmin) 
  xmin=v;
  fxmin=fv;
end

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%  Now, the main loop.  
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while ((newb-newa) > (tol* (1+(newa+newb)/2)))

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% Decide whether to move to [a,v] or [u,b]
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  if (fu < fv)
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%  New interval [a,v]
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    newb=v;
    fb=fv;
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%  Find the new v and u and evaluate the functions.
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    v=u;
    fv=fu;
    u=newa+0.3820*(newb-newa);
    fu=feval(fun,u);
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%  Update xmin and fxmin.
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    if (fu < fxmin) 
      xmin=u;
      fxmin=fu;
    end
  else
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%  New interval [u,b]
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    newa=u;
    fa=fu;
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%  Find the new v and u and evaluate the functions.
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    u=v;
    fu=fv;
    v=newa+0.6180*(newb-newa);
    fv=feval(fun,v);
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%  Update xmin and fxmin.
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    if (fv < fxmin) 
      xmin=v;
      fxmin=fv;
    end
  end
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% End the while loop.
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end