Function: ratcoef (<expr>, <x>, <n>)
Function: ratcoef (<expr>, <x>) Returns the coefficient of the expression
<x>^<n> in the expression <expr>. If omitted, <n> is assumed to be 1.
The return value is free (except possibly in a non-rational sense) of the variables in <x>. If no coefficient of this type exists, 0 is returned.
ratcoef expands and rationally simplifies its first argument and thus it may produce answers different from those of
coeff which is purely syntactic. Thus
ratcoef ((x + 1)/y + x, x) returns
(y + 1)/y whereas
coeff returns 1.
ratcoef (<expr>, <x>, 0), viewing <expr> as a sum, returns a sum of those terms which do not contain <x>. Therefore if <x> occurs to any negative powers,
ratcoef should not be used.
Since <expr> is rationally simplified before it is examined, coefficients may not appear quite the way they were envisioned.
(%i1) s: a*x + b*x + 5$ (%i2) ratcoef (s, a + b); (%o2) x
(%o1) true (%i2)