anchor.diff:  C----
   C Extract observed data from input time series
   C----
  -      open(unit=11,file=ifile,status='old')
  -      i = 1
  -  101 read(11,*,end=102) xobs(i),yobs(i)
  -          i = i + 1
  -          goto 101
  -  102 continue
  -      close(11)
  -      nobs = i - 1
  -
  +      if (ifile.ne.'stdin') then
  +          open(unit=11,file=ifile,status='old')
  +          i = 1
  +  101     read(11,*,end=102) xobs(i),yobs(i)
  +              i = i + 1
  +              goto 101
  +  102     continue
  +          close(11)
  +          nobs = i - 1
  +      else
  +          i = 1
  +  111     read(*,*,end=112) xobs(i),yobs(i)
  +              i = i + 1
  +              goto 111
  +  112     continue
  +          nobs = i - 1
  +      endif
   C----
   C Check if a constraint file was defined, and compute coefficients
   C----
  
positive.code:       endif
  
   9001 format('POLY_ORDER      COEFFICIENT')
   9002 format(I10,X,E16.6)
   9003 format(2E14.6)
  
        END
  
negative.code:       if (ifile.eq.'none') then
            write(*,*) '!! Error: Input x-y data is not specified'
            call usage('!! Use -f XYFILE to specify input file')
        elseif (ifile.ne.'stdin') then
            inquire(file=ifile,EXIST=ex)
            if (.not.ex) call usage('!! Error: no x-y file: '//ifile)
        endif
  