On 13.04.2021 11:35, Prof. Dr. Johannes Grabmeier privat wrote:
> the FriCAS code for inverting matrices over R is not correct. If wished
> I can provide the necessary changes to matfuns.spad
From my side, please do ;)
(2) -> IU := inverse(U)@Matrix(R)
An expression involving @ Matrix(IntegerMod(26)) actually evaluated
to one of type Union(Matrix(Fraction(Integer)),"failed") .
Perhaps you should use :: Matrix(IntegerMod(26)) .
(2) -> IU := inverse(U)::Matrix(R)
+1 24+
(2) | |
+0 1 +
Type: Matrix(IntegerMod(26))
)sh Matrix(R) => provides no inverse, indeed.
>
> Problem: recip returns "failed", inverse coerces to Fraction Integer:
>
> (1) -> R := IntegerMod 26
>
> (1) IntegerMod(26)
>
>
> Type: Type
>
> (2) -> U : Matrix R := [[1,2],[0,1]]
>
> +1 2+
> (2) | |
> +0 1+
>
> Type: Matrix(IntegerMod(26))
> (3) -> recip U
>
> (3) "failed"
>
> Type: Union("failed",...)
> (4) -> inverse U
>
> +1 - 2+
> (4) | |
> +0 1 +
> Type:
> Union(Matrix(Fraction(Integer)),...)
>
>
> The desired result should be the following:
>
> (72) -> inverse U
>
> +1 24+
> (72) | |
> +0 1 +
> Type:
> Union(Matrix(IntegerMod(26)),...)
>
>
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