Re: Question on using eval...

["Ruud H.G. van Tol" <rvtol@isolution.nl>]

On 2023-01-02 23:42, wraithx@morpheus.net wrote:
> On 1/2/2023 4:09 PM, Bill Allombert wrote:
> > On Mon, Jan 02, 2023 at 03:31:00PM -0600, wraithx@morpheus.net wrote:
> > > Hello,
> > >
> > > I've run into an issue using the "eval" function.  I'm trying to 
> > > check two
> > > expressions for symbolic equality.  But, I run into a problem when I 
> > > use the
> > > exponent operator.  Is this a valid use for the eval function?  Is 
> > > there
> > > another way to check if two expressions are equal?  Thank you for 
> > > any help
> > > you can provide!
> >
> > Dear David,
> >
> > The eval function does not work like in Maple.
> > Writing
> > ? eval("something")
> > has the same effect as
> > ? something.
> > so it is not useful with string constants.
> >
> > > gp > a
> > > %1 = a
> > > gp > b
> > > %2 = b
> > > gp > c
> > > %3 = c
> > > gp > eval("(a/b)+c == (a-b)+c")
> >
> >   gp> (a/b)+c == (a-b)+c
> >   would do the same thing faster.
>
> I did see that I could just write the expression on the gp command 
> line, but unfortunately, I am using code to generate these expressions 
> and so I only have them available as strings.
>
> Do you know of a way to compare two expressions in pari/gp (checking 
> for equality) when each expression is stored in a string?  Hopefully a 
> way that includes the exponent operator?

The "symbolic equality" also needs to be defined first.

? f(a,b,c) = (a / b) + c;
? g(a,b,c) = a / b + c;
? h(a,b,c) = c + a / b;
? print([f == g, f == h, g == h, g == f, f === g]);
[1, 0, 0, 1, 1]

-- Ruud