[Maxima-bugs] [maxima:bugs] Re: #4814 Default GCD algorithm can't handle algebraic

[David S. <tom...@us...>]

Totally fair point - silent fallbacks definitely make it harder to trace exactly which algorithm is doing the job under the hood.

I actually considered signaling an error, but decided against it for the following reason: Because `'$spmod` is Maxima's default `$gcd` setting, throwing an error would suddenly break standard user inputs. Anyone simply calling `gcd` on polynomials with `sqrt` or `%i` would get a hard error unless they knew to manually switch the algorithm to `'$subres`.

Maybe print a warning message? I'm just afraid that it would flood the console, because lots of GCDs are taken all the time.


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**[bugs:#4814] Default GCD algorithm can't handle algebraic**

**Status:** closed
**Group:** None
**Labels:** gcd algebraic 
**Created:** Sun Jul 12, 2026 11:56 AM UTC by David Scherfgen
**Last Updated:** Sun Jul 12, 2026 02:59 PM UTC
**Owner:** nobody


>From the manual:

> To take the gcd when an algebraic is present, e.g., `gcd (x^2 - 2*sqrt(2)* x + 2, x - sqrt(2))`, the option variable `algebraic` must be `true` and `gcd` must not be `ez`.

This example doesn't work with the default `gcd` value of `spmod`:

~~~
(%i1) gcd (x^2 - 2*sqrt(2)* x + 2, x - sqrt(2)), algebraic;
(%o1)                             x - sqrt(2)
~~~

We should probably automatically select a different algorithm when algebraics are present.


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