Re: [Maxima-discuss] elementary solve() problem

[Stavros M. <mac...@gm...>]

As Barton suggests, *solve* is weak in many ways. His *%solve *(in
*to_poly_solve*) is more powerful in many ways, but not all.

Some simple cases that neither one handles:

* *x!=0*
** x!=120*
* *sin(x)=x*
** 2^x=5^x*
* *7*2^x=5^x*

Many of these have easy solutions and also hard solutions with no closed
form. (Usually complex, but even some real ones: consider *x!* for *x<0* for
example.) Many users would be delighted for *solve *to find the easy
solutions, even if it can't find the hard solutions.

Tested in 5.48 SBCL 2.5.7 MacOS

On Thu, Nov 13, 2025 at 10:39 AM Barton Willis via Maxima-discuss <
max...@li...> wrote:

>
> The Maxima solve function needs improvement. Please don't get the
> impression that setting an obscure variable will fix all its shortcomings.
> Maybe somebody should experiment with making the default of solveradcan
>  true.
> --Barton
>
> ------------------------------
> *From:* richard christian <rp...@cl...>
> *Sent:* Thursday, November 13, 2025 5:33 AM
> *To:* Barton Willis <wi...@un...>
> *Cc:* max...@li... <
> max...@li...>
> *Subject:* Re: [Maxima-discuss] elementary solve() problem
>
> Caution: Non-NU Email
>
>
> Terrific. Thank you, Barton.
> And needless to say, apologies for the accidental repetition in the
> first 6 lines of my example...
>
> rc
>
> On 2025-11-13 11:23, Barton Willis wrote:
> > Try setting the option variable solveradcan to true before solving:
> >
> >  (%i1) solveradcan : true$
> >
> >  (%i2) solve(n*10^(n-1)=2*n*5^(n-1),n);
> >  (%o2) [n=0,n=2]
> >
> >  Alternatively, apply radcan before solving:
> >
> >  (%i1) radcan(n*10^(n-1)=2*n*5^(n-1));
> >  (%o1) 2^(n-1)*5^(n-1)*n=2*5^(n-1)*n
> >
> >  (%i2) solve(%,n);
> >  (%o2) [n=0,n=2]
> >
> >  For a list of additional option variables (and a bunch of other
> > stuff) that affect how solve works, try
> >
> >  (%i3) apropos (solve);
> >
> > (%o3)
> [desolve,funcsolve,globalsolve,linsolve,linsolve_by_lu,linsolve_params,linsolvewarn,solve,solve_congruences,solvedecomposes,solveexplicit,solvefactors,
> >
> >  Solvenullwarn,solveradcan,solvetrigwarn,tmlinsolve,to_poly_solve]
> >
> >  Thanks for your interest in Maxima! If you have more questions, feel
> > free to ask.
> >
> >  --Barton
> >
> > -------------------------
> >
> > From: richard christian <rp...@cl...>
> > Sent: Thursday, November 13, 2025 3:57 AM
> > To: max...@li...
> > <max...@li...>
> > Subject: [Maxima-discuss] elementary solve() problem
> >
> > Caution: Non-NU Email
> >
> > Apologies for this very novice question, but what am I doing wrong
> > here?
> > Why isn't Maxima giving n=2?
> >
> > (%i18)  s: t**n;
> > (s)     t^n
> > (%i19)  diff(s,t);
> > (%o19)  n*t^(n-1)
> > (%i20)  s: t**n;
> > (s)     t^n
> > (%i21)  diff(s,t);
> > (%o21)  n*t^(n-1)
> > (%i23)  ev(%,t=10) = 2*ev(%,t=5);
> > (%o23)  n*10^(n-1)=2*n*5^(n-1)
> > (%i24)  solve(%,n);
> > (%o24)  [n=0,10^(n-1)=2*5^(n-1)]
> >
> > Many thanks, Richard
> >
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