stellinstall/dnherm1_8f_source.html

      subroutine dnherm1(x,nx,fherm,ilinx,ier)

C

C  create a data set for Hermite interpolation, based on simple

C  numerical differentiation using the given grid.

C

C  1d routine

C

C  input:

C

      integer nx                        ! array dimensions

      real x(nx)                        ! x coordinate array

      real fherm(0:1,nx)                ! data/Hermite array

C

C  fherm(0,i) = function value f at x(i)       **on input**

C

C  fherm(1,i) = derivative df/dx at x(i)       **on output**

C

C addl output:

C  ilinx=1 if x is "evenly spaced" ier=0 if no errors

C

C  ** x must be strict ascending **

C

C----------------------------

C

      ztol=1.0e-3

      call splinck(x,nx,ilinx,ztol,ier)

      if(ier.ne.0) then

         write(6,*) '?dnherm1:  x axis not strict ascending.'

         return

      endif

C

      do ix=1,nx

c

c  x div. diffs in vicinity

c

         ixp=min(nx,ix+1)

         ixm=max(1,ix-1)

         zd=(fherm(0,ixp)-fherm(0,ixm))/(x(ixp)-x(ixm))

c

         fherm(1,ix)=zd

      enddo

C

      return

      end