source: PSPA/parmelaPSPA/trunk/spl1d2.f @ 404

      subroutine spl1d2(n,x,f,w,ij,y,tab)
c     where n= number of points in the interpolation
c           x= origin of table of the independent variable
c           f= origin of table of the dependent variable
c           w= origin of table of second derivatives as calculated by
c              spl1d1
c          ij= spacing in the tables f and w
c           y= the point at which interpolation is desired
c         tab= an array of dimension 3 which contains the function
c              value, first derivative, and second derivative at y
c--------------------------------------------------------------------------
c
      dimension x(n),f(n),w(n),tab(3)
c--------------------------------------------------------------------------
c*
c
c     locate y in the x table
      call interv (x,n-1,y,i)
   30 mi=(i-1)*ij+1
      k1=mi+ij
      flk=x(i+1)-x(i)
c
c     calculate f(y)
c
      a=(w(mi)*(x(i+1)-y)**3+w(k1)*(y-x(i))**3)/(6.*flk)
      b=(f(k1)/flk-w(k1)*flk/6.)*(y-x(i))
      c=(f(mi)/flk-flk*w(mi)/6.)*(x(i+1)-y)
      tab(1)=a+b+c
c
c     calculate the first derivative at y
c
      a=(w(k1)*(y-x(i))**2-w(mi)*(x(i+1)-y)**2)/(2.*flk)
      b=(f(k1)-f(mi))/flk
      c=flk*(w(mi)-w(k1))/6.
      tab(2)=a+b+c
c
c     calculate the second derivative at y
c
      tab(3)=(w(mi)*(x(i+1)-y)+w(k1)*(y-x(i)))/flk
      return
      end
c+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++