[Maxima-bugs] [maxima:bugs] #4169 spmod bug when algebraic is true

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

- **status**: open --> closed
- **Comment**:

Fixed by commit	[948338].



---

**[bugs:#4169] spmod bug when algebraic is true**

**Status:** closed
**Group:** None
**Labels:** gcd spmod algebraic 
**Created:** Wed Aug 02, 2023 12:33 PM UTC by Barton Willis
**Last Updated:** Wed Aug 02, 2023 12:36 PM UTC
**Owner:** nobody


Here is a bug that manifests when `gcd = spmod` and `algebraic = true.` Define `p` and  `dp`

~~~
(%i1)	p : gfactor(-((z-1)*(2*z-%i-2)^2));
(%o1)	-(z-1)*(2*z-%i-2)^2

(%i2)	dp : gfactor(diff(p,z));
(dp)	-(2*z-%i-2)*(6*z-%i-6)
~~~

Both are OK
~~~
(%i3)	block([gcd : subres, algebraic : false], gcd(p,dp));
(%o3)	2*z-%i-2

(%i4)	block([gcd : subres, algebraic : true], gcd(p,dp));
(%o4)	2*z-%i-2
~~~

Wrong for `gcd = spmod` and `algebraic = true`
~~~
(%i5)	block([gcd : spmod, algebraic : true], gcd(p,dp));
(%o5)	1
~~~

But OK for `gcd = spmod` and `algebraic = false`
~~~
(%i6)	block([gcd : spmod, algebraic : false], gcd(p,dp));
(%o6)	2*z-%i-2
~~~


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