[LON-CAPA-users] coding a customresponse problem using &cas()
Gerd Kortemeyer
kortemey at msu.edu
Wed May 27 07:41:26 EDT 2015
Hi,
> On May 26, 2015, at 10:36 PM, Damien Guillaume <damieng at msu.edu> wrote:
>
>> This seems to work as expected for square matrices. However, the example
>> below accepts ([2,-2,-4],[-1,3,4]) as an answer, even though
>> &cas('maxima','rank(matrix'.$submission.'^^2-matrix'.$submission.')')
>> should generate an error in MAXIMA:
>>
>> (%i1) A:matrix([2,-2,-4],[-1,3,4]); [ 2
>> - 2 - 4 ]
>> (%o1) [ ]
>> [ - 1 3 4 ]
>> (%i2) rank(A^^2 - A);
>> MULTIPLYMATRICES: attempt to multiply nonconformable matrices.
>> -- an error. To debug this try: debugmode(true);
>
> It looks like maximareply() in lonmaxima.pm does not recognize this error message as an error message (it is only checking if there is "incorrect" in the reply). I guess the best solution would be to fix that, but maybe there is a way to tell if the result of the cas call makes sense or not (like testing if it is an integer), as a workaround.
Argh! Yes, it’s really a problem that MAXIMA was designed throughout for interactive sessions. The replies are non-standardized.
I am not sure if &maximareply() gives us back the whole message, since it is two lines (another problem), so I think we only get back “MULTIPLYMATRICES: attempt …” It is impossible to anticipate all the possible messages that MAXIMA returns, since there is no standard - each package spits out whatever the author imagined. In this case, probably the only remedies are to interpret the presence of “attempt” also as an error
if ($determinant=~/(error|attempt)/i) { return ‘BAD_FORMULA’; }
or to see if we only get back a number
unless ($determinant=~/^\s*\d+\s*$) { return ‘BAD_FORMULA’; }
- probably cleaner to do the latter, if we know that all ranks should just be numbers.
- Gerd.
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