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

[David S. <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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