On Monday, 14 May 2012 15:50:07 UTC+1, jg wrote:
>
> Hallo Paul, 
>
> this is not a problem of the Finite Field code (which I contributed to 
> very long ago) and to find the error, it is also not neccessary to 
> encapsulate in new domains as your MYFF etc.


I created the MYFF and MYFFX domains so that I could control exactly how 
they differ. When called from my input file, the only difference really was 
where the PrimeField(2) constructor was called: for MYFF it is called in 
the MYFF constructor, for MYFFX it is called by the interpreter and the 
result passed to the MYFFX constructor.

It is indeed a problem of function selection of the interpreter. Use: 
>
> )set mess sel on
>

Ahh, so that's the magic incantation I needed, thanks. 
 

> The reason is the following: rem and quo are defined for Euclidean 
> Domains, which Polynomial of a Field is not. 
> Therefore, if you change your variable definition to e.g. 
>
> p : UP(x. MYFFX) := a*x+1 
>
> etc. it will work! The interpreter has no extra work todo. 
>

Yes, that's what I ended up doing to get things working 9 months ago.
 
< ... >

>
> However, for strange reason: THIS PROBLEM MUST BE HANDED TO EXPERTS OF THE 
> INTERPRETER FUNCTION SELECTION FACILITIES AND COERCION FACILITIES, 
> the interpreter - in case of FFX(PF 2, 4) finds a coefficent 
> coercion/retraction to transfer to POLY(PF 2) using a retraction (partial 
> function) to the prime field, which is 
> here explicitly exhibited in FFX contrary to FF, where this is hidden for 
> the interpreter I guess. For some strange reason, the heurisitic seems to 
> think that transfer the problem to POLY PF 2, it will solve it from there. 
> Actually this is not the case, as the transfer to the Polynomials over the 
> prime field must fail (your observed error message). 
>

Okay, I wonder how difficult it is to understand the interpreter... :-o

Thanks very much for your help,
Paul

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