program volgrad2
c
c	second scheme: subtractions from the working volume
c
c	calculate volume steps for changing from 0% B to 100% B
c	with a working volume of X in Y steps
c	volgrad X Y
c	e.g. "volgrad 200 10 >file" will print steps for changing to 100% B
c	in 10 steps with a working volume of 200 (ul or whatever)
c
c
        integer n_arg, iargc
	integer nsteps, step, tempi, i
	real workvol, remvol, tempvol, conc, prev_conc
	character*80 line
c
	data workvol, nsteps, volume / 100.0, 10, 0.0 /
c

c
c               look for command line arguments
        n_arg = iargc()
        if (n_arg .NE. 0) then
c	    recover volume
            call getarg(1, line)
	    read(line, *, end=666, err=666) tempvol
	      workvol = tempvol
	  if (n_arg .gt. 1) then
c	    recover # steps
	    call getarg(2, line)
	    read(line, *, end=666, err=666) tempi
	    nsteps = tempi
	  endif
	endif

	if (nsteps .lt. 0 .or. volume .lt. 0.0) then
	  write(6,*) ' volume= ', workvol, '  number of steps= ', nsteps
	  stop ' VOLGRAD> bad input'
	endif

c	write out header
	write(6,'(A)') ' Switching from 0% B to 100% B'
	write(6,101) workvol, nsteps
 101	format(' with a working volume of  ',F6.1,' in ',I4,' steps')
	write(6,*) ' subtraction scheme'
	write(6,*)
	write(6,*) ' Starting volume:', workvol
	conc      = 0.0
	prev_conc = 0.0
	rem_vol   = 0.0

	do i = 1, nsteps
	  write(6,*) 
	  write(6,*) ' STEP ', i
	  prev_conc = conc
	  conc = ( real(i) / real(nsteps) ) * 100
	  remvol = ( workvol* (conc - prev_conc) ) / ( 100.0 - prev_conc )
	  write(6,*) ' remove ', remvol
	  write(6,102) conc
 102	format( ' new target concentration: ',F5.1,'%')
	  write(6,*) ' add ', remvol, ' of 100% B'

	end do		!nsteps

	goto 669

 666	continue
	stop 'VOLGRAD> bad command line argument'
c
 669	continue
c	successful completion, terminate
	end