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5.1.137 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
See defined; ring; var; varstr.