5.1.139 rvar

Syntax:

rvar ( name )
rvar ( poly_expression )
rvar ( string_expression )

Type:

int

Purpose:

returns the number of the variable if the name/polynomial is a ring variable of the basering or if the string is the name of a ring variable of the basering; returns 0 if not. Hence the return value of rvar can also be used in a boolean context to check whether the variable exists.

Example:

ring r=29,(x,y,z),lp; rvar(x); ==> 1 rvar(r); ==> 0 rvar(y); ==> 2 rvar(var(3)); ==> 3 rvar("x"); ==> 1