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Re: [Axiom-mail] Inverting a matrix over a modular integer ring
From: |
Martin Rubey |
Subject: |
Re: [Axiom-mail] Inverting a matrix over a modular integer ring |
Date: |
27 May 2007 12:07:57 +0200 |
User-agent: |
Gnus/5.09 (Gnus v5.9.0) Emacs/21.4 |
"Alasdair McAndrew" <address@hidden> writes:
> Suppose I create the matrix
>
> M:=matrix([[random()$PF(19) for i in 1..3] for j in 1..3])
>
> Assuming the determinant is non-zero, then I can invert the matrix in the
> finite field PF(19). But suppose I enter
>
> N:=matrix([[random()$ZMOD(20) for i in 1..3] for j in 1..3])
>
> If the determinant is relatively prime to 20, then the inverse of N exists
> over the ring ZMOD(20). But division is not defined in ZMOD - so how do I
> invert N?
Look up ZMOD in HyperDoc! recip is your friend (works for all Monoids, I
think)
Martin