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subroutine lsdisc (f, neq, y, t, tout, rwork,lrw,istate )
external f
integer neq, lrw
double precision y(neq), t, tout, rwork(lrw)
c!purpose
c
c Simulation of non linear recurrence equations of type
c x[k+1]=f(k,xk)
c
c!summary of usage.
c a. first provide a subroutine of the form..
c subroutine f (neq, t, y, ydot)
c dimension y(neq), ydot(neq)
c which supplies the vector function f by loading ydot(i) with f(i).
c
c f = name of subroutine for right-hand side vector f.
c this name must be declared external in calling program.
c neq = number of first order ode-s.
c y = array of initial values, of length neq.
c t = the initial value of the independent variable.
c tout = first point where output is desired
c istate = 2 if lsdisc was successful, negative otherwise.
C
C # cases according to the difference between t and tout
C
c!
c-----------------------------------------------------------------------
integer it,itout
double precision tt
integer iero
common /ierode/ iero
include '../stack.h'
c
it=int(t)
itout=int(tout)
iero=0
if ( itout.lt.it) then
buf ='ode discrete : a requested k is smaller '
$ // ' than initial one'
call error(999)
return
else if ( itout.eq.it) then
istate=2
return
else
do 10 j=it,itout-1
tt=dble(j)
call f (neq,tt, y, rwork)
if(iero.gt.0) return
call dcopy(neq,rwork,1,y,1)
10 continue
t=tout
istate=2
return
endif
end
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