zroots.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 zroots(a,m,roots,polish)
      INTEGER m,MAXM
      REAL EPS
      COMPLEX a(m+1),roots(m)
      LOGICAL polish
      PARAMETER (EPS=1.e-6,MAXM=101)
CU    USES laguer
      INTEGER i,j,jj,its
      COMPLEX ad(MAXM),x,b,c
      do 11 j=1,m+1
        ad(j)=a(j)
11    continue
      do 13 j=m,1,-1
        x=cmplx(0.,0.)
        call laguer(ad,j,x,its)
        if(abs(aimag(x)).le.2.*EPS**2*abs(real(x))) x=cmplx(real(x),0.)
        roots(j)=x
        b=ad(j+1)
        do 12 jj=j,1,-1
          c=ad(jj)
          ad(jj)=b
          b=x*b+c
12      continue
13    continue
      if (polish) then
        do 14 j=1,m
          call laguer(a,m,roots(j),its)
14      continue
      endif
      do 16 j=2,m
        x=roots(j)
        do 15 i=j-1,1,-1
          if(real(roots(i)).le.real(x))goto 10
          roots(i+1)=roots(i)
15      continue
        i=0
10      roots(i+1)=x
16    continue
      return
      END