denom

Denominator of a rational expression

Use only in the MuPAD Notebook Interface.

This functionality does not run in MATLAB.

Syntax

denom(f)

Description

denom(f) returns the denominator of the expression f.

denom regards the input as a rational expression: non-rational subexpressions such as sin(x), x^(1/2) etc. are internally replaced by "temporary variables". The denominator of this rationalized expression is computed, the temporary variables are finally replaced by the original subexpressions.

    Note:   Numerator and denominator are not necessarily cancelled: the denominator returned by denom may have a non-trivial gcd with the numerator returned by numer. Pre-process the expression by normal to enforce cancellation of common factors. Cf. Example 2.

Examples

Example 1

We compute the denominators of some expressions:

denom(-3/4)

denom(x + 1/(2/3*x -2/x))

denom((cos(x)^2 -1)/(cos(x) -1))

Example 2

denom performs no cancellations if the rational expression is of the form "numerator/denominator":

r := (x^2 - 1)/(x^3 - x^2 + x - 1): denom(r)

This denominator has a common factor with the numerator of r; normal enforces cancellation of common factors:

denom(normal(r))

However, automatic normalization occurs if the input expression is a sum:

denom(r + x/(x + 1) + 1/(x + 1) - 1)

delete r:

Parameters

f

An arithmetical expression

Return Values

Arithmetical expression.

Overloaded By

f

See Also

MuPAD Functions

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