How to simplify cos(pi)?

Question

I'am new to Maxima and would like to use it for Denavit-Hartenberg matrices (consists of a lot of cos and sin terms). The problem is, that maxima does not simplify the following expression:

ex: x*cos(pi);

I expect, that Maxima simplifies ex to -x. How can this been done? (ratsimp(ex) and trigsimp(ex) have no effects)

@RobertHarvey, he knows ("I expect that Maxima simplifies `ex` to `-x`"). — zneak, Apr 11 '13 at 19:11
The Maxima documentation shows a lot of expression manipulation functions [here](http://eagle.cs.kent.edu/MAXIMA/maxima_15.html). Trigsimp does painfully little to simplify that kind of expression. (Also, they use `%pi` instead of `pi`.) — zneak, Apr 11 '13 at 19:13
Thank you! wxMaxima displays `pi` as the greek letter, so I supposed that this is the right constant. With `%pi` Maxima simplifies it correct without additional work :) — Vertex, Apr 11 '13 at 19:41

score 9 · Accepted Answer · answered Apr 12 '13 at 15:11

9

In Maxima's dialect, the correct name of the constant is %pi. With it, it should simplify correctly.

answered Apr 12 '13 at 15:11

zneak

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score 3 · Answer 2 · edited Aug 02 '15 at 20:16

As others have said, %pi is the correct name of the constant in Maxima. pi is simply rendered as π in GUIs like wxMaxima because all Greek letters are (you can have a variable named "π", which has nothing to do with the value of the constant π=3.14159...).

By the way, other predefined constants are written with the % character as well, such as for example

%e (=exp(1))
%i (=sqrt(-1))
%phi (the golden section)

The manual's index lists all % candidates.

Note that other useful constants that can not be expressed by digits, such as inf or false do not have the percent character.

How to simplify cos(pi)?

2 Answers2