# [Maxima] Difference between array and matrix and usage of "~"

Robert Dodier robert.dodier at gmail.com
Tue Nov 13 22:58:28 CST 2007

On 11/13/07, 姓 ���� <tianjh04 at mails.tsinghua.edu.cn> wrote:

> (C1) load(vect)\$
> (C2) A : matrix([1,2,3], [4,5,6])\$
> (C3) row(A,1) ~ row(A,2);
> (D3)                       [ 1  2  3 ] ~ [ 4  5  6 ]
> (C4) express(row(A,1) ~ row(A,2));
> ~ USED WITH IMPROPER ARGUMENTS: [ 1  2  3 ] [ 4  5  6 ]

A[k] is the k'th row of the matrix, a list. Try this:

express (A[1] ~ A[2]);

> 2. zero vector returned from "~" simply "shrinks" to scalar zero:
>
> (C1) [1,1,1] ~ [1,1,1];
> (D1)                                               0
>
> Why isn't it [0,0,0]?

I agree, it should be [0, 0, 0]. I will see if there is some interest in
changing the vect package.

Until then, you can try this:

simp : false;
matchdeclare (aa, all);
tellsimp (aa ~ aa, [0, 0, 0]);
tellsimp ([0, 0, 0] ~ aa, [0, 0, 0]);
tellsimp (aa ~ [0, 0, 0], [0, 0, 0]);
simp : true;

[1, 1, 1] ~ [1, 1, 1];
=> [0, 0, 0]

By the way, it appears you have a very old version of Maxima
(maybe 3 or 4 years old). I recommend that you get a more
recent version; there have been many bug fixes and other
improvements.

best

Robert Dodier

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