qroot.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 qroot(p,n,b,c,eps)
      INTEGER n,NMAX,ITMAX
      REAL b,c,eps,p(n),TINY
      PARAMETER (NMAX=20,ITMAX=20,TINY=1.0e-6)
CU    USES poldiv
      INTEGER iter
      REAL delb,delc,div,r,rb,rc,s,sb,sc,d(3),q(NMAX),qq(NMAX),rem(NMAX)
      d(3)=1.
      do 11 iter=1,ITMAX
        d(2)=b
        d(1)=c
        call poldiv(p,n,d,3,q,rem)
        s=rem(1)
        r=rem(2)
        call poldiv(q,n-1,d,3,qq,rem)
        sc=-rem(1)
        rc=-rem(2)
        sb=-c*rc
        rb=sc-b*rc
        div=1./(sb*rc-sc*rb)
        delb=(r*sc-s*rc)*div
        delc=(-r*sb+s*rb)*div
        b=b+delb
        c=c+delc
        if((abs(delb).le.eps*
     *abs(b).or.abs(b).lt.TINY).and.(abs(delc).le.eps*
     *abs(c).or.abs(c).lt.TINY)) return
11    continue
      pause 'too many iterations in qroot'
      END