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logical function israt(il,ilnum,ilden,ildom)
c given a scilab variable stored in the stack, beginning at istk(il)
c israt checks is this variable is a rational fraction
c if ok it also returns ilnum and ilden the adress of the beginning
c of the variables (in istk) containing the numerator and the denominator
c Copyright INRIA
INCLUDE '../stack.h'
integer iadr, sadr
c
iadr(l)=l+l-1
sadr(l)=(l/2)+1
c
israt=.false.
c check if variable is a tlist
if(istk(il).ne.16) return
c check if tlist has 4 elements
if(istk(il+1).ne.4) return
c check if first element is a character string vector
ll=sadr(il+7)
ill=iadr(ll)
if(istk(ill).ne.10) return
c check if first entry of the character string vector is 'r'
if(abs(istk(ill+5+istk(ill+1)*istk(ill+2))).ne.27) return
c check second and third tlist components
ilnum=iadr(ll+istk(il+3)-1)
if(istk(ilnum).gt.2) return
ilden=iadr(ll+istk(il+4)-1)
if(istk(ilden).gt.2) return
ildom=iadr(ll+istk(il+5)-1)
israt=.true.
return
end
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