Dear Zoltan,
I have also observed the same behaviour on Windows and I feel this
is normal for Maxima in the way the computations are done although
I do not know any of the details of these computations. Exactly as you
did, I also received from Maxima:
(C1) is(equal(sin(x)/cos(x), tan(x)));
MACSYMA was unable to evaluate the predicate:
ERREXP1
-- an error. Quitting. To debug this try DEBUGMODE(TRUE);)
In my impression, it seems that Maxima requires that both members
of equal be exactly the same in is and this is possible in the present
trigonometric functions with the devoted (not just the standard)
simplification command, which is trigsimp.
(C2) is(equal(sin(x)/cos(x), trigsimp(tan(x))));
(D2) TRUE
Personally, I prefer to use the = sign (a not exactly equivalent
approach)
(C3) is(sin(x)/cos(x) = tan(x));
(D3) FALSE
(C4) is(sin(x)/cos(x) = trigsimp(tan(x)));
(D4) TRUE
in order to get just false (before the trigonometric simplification) or
true (after the trigonometric simplification) instead of an error. In
my opinion, this is preferable in the is command.
Moreover, as I have read, avoiding this error is possible even with
the equal command with the prederror switch:
(C10) prederror : false$
(C11) is(equal(sin(x)/cos(x), tan(x)));
(D11) UNKNOWN
(C12) is(equal(sin(x)/cos(x),trigsimp(tan(x))));
(D12) TRUE
Perhaps, this is a preferable behaviour.
Best regards,
Nikos
> --- "kovzol" <kovzol@math.u-szeged.hu> wrote:
> now I'm having a problem with IS(). I'd like to know whether
> sin(x)/cos(x)=tan(x). I'm writing:
>
> IS(EQUAL(sin(x)/cos(x),tan(x)));
>
> Maxima reports an error:
>
> MACSYMA was unable to evaluate the predicate:
> ERREXP1
> -- an error. Quitting. To debug this try DEBUGMODE(TRUE);)
>
> Is this the normal behaviour?
>
> TIA, Zoltan
>
> Kova'cs Zolta'n
> assistant teacher at Bolyai Institute