amebsa.for

Numerical Recipes一书中例子的源码所用到的函数集,William H. Press 和 Saul A. Teukolsky 所著

      SUBROUTINE amebsa(p,y,mp,np,ndim,pb,yb,ftol,funk,iter,temptr)
      INTEGER iter,mp,ndim,np,NMAX
      REAL ftol,temptr,yb,p(mp,np),pb(np),y(mp),funk
      PARAMETER (NMAX=200)
      EXTERNAL funk
CU    USES amotsa,funk,ran1
      INTEGER i,idum,ihi,ilo,inhi,j,m,n
      REAL rtol,sum,swap,tt,yhi,ylo,ynhi,ysave,yt,ytry,psum(NMAX),
     *amotsa,ran1
      COMMON /ambsa/ tt,idum
      tt=-temptr
1     do 12 n=1,ndim
        sum=0.
        do 11 m=1,ndim+1
          sum=sum+p(m,n)
11      continue
        psum(n)=sum
12    continue
2     ilo=1
      inhi=1
      ihi=2
      ylo=y(1)+tt*log(ran1(idum))
      ynhi=ylo
      yhi=y(2)+tt*log(ran1(idum))
      if (ylo.gt.yhi) then
        ihi=1
        inhi=2
        ilo=2
        ynhi=yhi
        yhi=ylo
        ylo=ynhi
      endif
      do 13 i=3,ndim+1
        yt=y(i)+tt*log(ran1(idum))
        if(yt.le.ylo) then
          ilo=i
          ylo=yt
        endif
        if(yt.gt.yhi) then
          inhi=ihi
          ynhi=yhi
          ihi=i
          yhi=yt
        else if(yt.gt.ynhi) then
          inhi=i
          ynhi=yt
        endif
13    continue
      rtol=2.*abs(yhi-ylo)/(abs(yhi)+abs(ylo))
      if (rtol.lt.ftol.or.iter.lt.0) then
        swap=y(1)
        y(1)=y(ilo)
        y(ilo)=swap
        do 14 n=1,ndim
          swap=p(1,n)
          p(1,n)=p(ilo,n)
          p(ilo,n)=swap
14      continue
        return
      endif
      iter=iter-2
      ytry=amotsa(p,y,psum,mp,np,ndim,pb,yb,funk,ihi,yhi,-1.0)
      if (ytry.le.ylo) then
        ytry=amotsa(p,y,psum,mp,np,ndim,pb,yb,funk,ihi,yhi,2.0)
      else if (ytry.ge.ynhi) then
        ysave=yhi
        ytry=amotsa(p,y,psum,mp,np,ndim,pb,yb,funk,ihi,yhi,0.5)
        if (ytry.ge.ysave) then
          do 16 i=1,ndim+1
            if(i.ne.ilo)then
              do 15 j=1,ndim
                psum(j)=0.5*(p(i,j)+p(ilo,j))
                p(i,j)=psum(j)
15            continue
              y(i)=funk(psum)
            endif
16        continue
          iter=iter-ndim
          goto 1
        endif
      else
        iter=iter+1
      endif
      goto 2
      END