Re: [Maxima-discuss] How can I catch this error? "errcatch" doesn't do the trick.

[David S. <d.s...@go...>]

Oops, make that sinint.lisp, not sin.lisp!

2015-09-08 21:58 GMT+02:00 David Scherfgen <d.s...@go...>:

> Thanks, Robert!
>
> I also have a patch for the integrate_use_rootsof bug. I can't believe I
> actually found the spot in the code, even though I don't really understand
> LISP. :-)
>
> All we need to do is to use a different variable inside the rootsof
> expression, not the original variable of integration. This prevents the
> back-substitution at the end of the integration.
>
> Here's a possible way to do that:
>
> src/sin.lisp, line 169:
> - (($rootsof) ,qq))))
> + (($rootsof) ,(subst (make-param) variable qq)))))
>
> (%i1) integrate(1/(x^(1/3)+x+1),x),integrate_use_rootsof:true;
> (%o1)
> 3*'lsum((%r1^2*log(x^(1/3)-%r1))/(1+3*%r1^2),%r1,rootsof(%r2^3+%r2+1))
>
> As you see, there are now two auxiliary variables, %r1 and %r2. Maybe the
> second one should get a different prefix? I don't know if there is any kind
> of guideline for that.
>
> If somebody gives me the permission, I would gladly make this my very
> first Git commit to Maxima.
>
> Kind regards,
> David
>
> 2015-09-08 21:47 GMT+02:00 Robert Dodier <rob...@gm...>:
>
>> On 2015-09-07, David Scherfgen <d.s...@go...> wrote:
>>
>> > the following integral results in an error "quotient by zero":
>> >
>> > integrate(ev(ratsimp(1/(x^(5/2)+3*x^(1/3))),algebraic),x);
>> >
>> > Unfortunately, I can't catch the error using errcatch. It goes right
>> > through it, i.e. the whole evaluation is aborted, and I don't get any
>> > result (usually, errcatch would give me an empty list if it caught an
>> > error).
>>
>> When "quotient by zero" is encountered, 'RAT-ERR is thrown, which blows
>> through 'catch' and 'errcatch'. I believe that's a bug.
>>
>> A solution is to call RAT-ERROR-TO-MERROR in 'catch' and 'errcatch'. I
>> got that from TOPLEVEL-MACSYMA-EVAL. From what I can tell, that makes
>> 'errcatch' work as expected for the above example (i.e., return an empty
>> list) and obviates the need for redefining MERROR.
>>
>> best,
>>
>> Robert Dodier
>>
>> PS. Here is a patch.
>> diff --git a/src/suprv1.lisp b/src/suprv1.lisp
>> index d0c5fa4..be0a59f 100644
>> --- a/src/suprv1.lisp
>> +++ b/src/suprv1.lisp
>> @@ -770,14 +770,14 @@
>>  (defmspec $errcatch (form)
>>    (let ((errcatch (cons bindlist loclist)) ret)
>>      (if (null (setq ret (let (*mdebug*)
>> -                         (errset (mevaln (cdr form)) lisperrprint))))
>> +                         (errset (rat-error-to-merror (mevaln (cdr
>> form))) lisperrprint))))
>>         (errlfun1 errcatch))
>>      (cons '(mlist) ret)))
>>
>>  (defmspec $catch (form)
>>    (let ((mcatch (cons bindlist loclist)))
>>      (prog1
>> -       (catch 'mcatch (mevaln (cdr form)))
>> +       (catch 'mcatch (rat-error-to-merror (mevaln (cdr form))))
>>        (errlfun1 mcatch))))
>>
>>  (defmfun $throw (exp)
>>
>>
>>
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>