#424 IS often doesn't work

[Jonas Diemer]

Hi!

The IS function is used to evaluate if an expression is
true, correct? It doesn't seem to like equations that
are not factored out:

2*(x-(y+x))=2*x-2*(y+x);

should be true, right? IS sais, it wasn't.

Jonas

PS: I am not an expert in CAS. If I reported complete
bullshit, I would be happy about a short explanation
why. thanks in advance.

[Stavros Macrakis]

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user_id=588346

In Maxima, is(...=...) tests for *syntactic* equality: the two
expressions have the same structure. To test for *semantic*
equality, use equal.

In your example, is(equal(2*(x-(y+x)),2*x-2*(y+x)) returns
true as you'd expect.

That said, in many cases is/equal cannot determine the
correct result, even if other parts of Maxima can -- e.g. is
(equal(sin(x)^2+cos(x)^2,1)).

I agree that this is confusing, but this is the intended
behavior.

[Jonas Diemer]

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user_id=154672

I see. Maybe somthing about testing equality etc. could go
in the Primer or somewhere else...

Regards