#4605 askinteger extremely weak

[Barton Willis]

askinteger/featurep(...,integer) is very weak.

makelist(featurep(q,'integer),
   [(-1)^ii, ii*(ii+1)/2, sin(ii*%pi/2), ii+1/2, %pi*ii,
     sin(ii), log(ii), %e^ii, %i*%pi])
     => [false, false, false, false, false,
                false, false, false, false]
 ~~~

 ``askinteger`` is equally weak. 

This is OK:

(%i2) featurep(%i*%pi,'integer);
(%o2)                                false

[David Scherfgen]

Maybe askinteger should check the imagpart of the expression and say "no" when it's certain to be non-zero.

[Stavros Macrakis]

askinteger is extremely weak. With declare(ii,integer)$ ,

it doesn't know that all of the following are always integer-valued:

(-1)^ii

ii*(ii+1)/2

sin(ii*%pi/2)

and that the following are never integer-valued:

ii+1/2

%pi*ii

sin(ii)

log(ii)

%e^ii

All of these seem much more likely to arise "in the wild" and be useful to
users than the %i*%pi case. I have generalized
https://sourceforge.net/p/maxima/bugs/4605/ to include them.

      -s

On Wed, Sep 3, 2025 at 1:26 PM David Scherfgen via Maxima-bugs maxima-bugs@lists.sourceforge.net wrote:

Maybe askinteger should check the imagpart of the expression and say "no"
when it's certain to be non-zero.

---

[bugs:#4605] https://sourceforge.net/p/maxima/bugs/4605/
askinteger(%i%pi)*

Status: open
Group: None
Created: Mon Sep 01, 2025 04:49 PM UTC by Barton Willis
Last Updated: Mon Sep 01, 2025 04:49 PM UTC
Owner: nobody

Not wrong, but far from optimal

(%i1) askinteger(%i*%pi);
Is %i %pi an integer?

no;
(%o1) no

This is OK:

(%i2) featurep(%i*%pi,'integer);
(%o2) false

---

Sent from sourceforge.net because maxima-bugs@lists.sourceforge.net is
subscribed to https://sourceforge.net/p/maxima/bugs/

To unsubscribe from further messages, a project admin can change settings
at https://sourceforge.net/p/maxima/admin/bugs/options. Or, if this is a
mailing list, you can unsubscribe from the mailing list.

---

Maxima-bugs mailing list
Maxima-bugs@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/maxima-bugs