Re: Inverting a matrix over a modular integer ring

"Alasdair McAndrew" <[email protected]> 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