rtnewt.f90

来自「FORTRANvisualfortran常用数值算法集及源码」· F90 代码 · 共 19 行

FUNCTION rtnewt(funcd,x1,x2,xacc)
INTEGER JMAX
REAL rtnewt,x1,x2,xacc
EXTERNAL funcd
PARAMETER (JMAX=20)
INTEGER j
REAL df,dx,f
rtnewt=.5*(x1+x2)
do j=1,JMAX
  call funcd(rtnewt,f,df)
  dx=f/df
  rtnewt=rtnewt-dx
  if((x1-rtnewt)*(rtnewt-x2)<0.) pause
!rtnewt jumped out of brackets'
  if(abs(dx)<xacc) return
end do
pause 'rtnewt exceeded maximum iterations'
END FUNCTION rtnewt