improve gcd documentation for %i and other algebraics

[rtoy]

Imported from SourceForge on 2024-07-09 20:03:00
Created by macrakis on 2023-12-28 20:32:27
Original: https://sourceforge.net/p/maxima/bugs/4232

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gcd doc currently reads:

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

• Actually, gcd must be either subres or red; neither ez nor spmod handles the algebraic case. Test:

 makelist( gcd (x^2-2, x-sqrt(2)),
         gcd,'[ez,subres,red,spmod]),algebraic;
    => [1, x - sqrt(2), x - sqrt(2), 1]

• Instead of saying "must not be ez, it is clearer, simpler, and more accurate to say "must be subres or red".

• We should explicitly mention that taking the GCD over the complexes (C) is included in the algebraic case:

makelist( gcd(x^2+1,x+%i),
       gcd, '[ez,subres,red,spmod]),algebraic;
   => [1, x + %i, x + %i, 1]

Tested in Maxima 5.46.0 SBCL 2.3.0 MacOS