subroutine  calc_f(f,  q)

c------------------------------------------------------------
c Calculates the physical jumps for c Burger's equation from 
c the reconstructed variables.
c------------------------------------------------------------

         implicit      none

         character*6   cdnm
         parameter   ( cdnm = 'calc_f' ) 

         logical       ltrace
         parameter   ( ltrace = .false. )

         real*8       f,     q

c============================================================
c============================================================
         if ( ltrace ) then
            write(0,*) cdnm,':   q= ', q
         endif
         f = 0.5d0*q**2
         if ( ltrace ) then
            write(0,*) cdnm,':   f= ',f
         endif
         return
         end