A regression in Maxima 5.17.1 with limits and assumptions?

?Why behaviour in limit of a product:

? you know that limit a * b = lim a * lim b but when there is inf or minf you have to 
know the behaviour (sign) of the factors? in order to compute the sign of the product,
?that is inf or minf.? A possible work around this is only asking the sign when a inf or minf factor appear, but the problem is that the inf can appear later, so keep a list of 
factors, compute the limit of each, trigger a flag if some inf or minf is involved and ask sign in this situations.

?Only guessing here.


--- El lun, 22/12/08, Raymond Toy <raymond.toy at ericsson.com> escribi?:
De: Raymond Toy <raymond.toy at ericsson.com>
Asunto: Re: [Maxima] A regression in Maxima 5.17.1 with limits and assumptions?
Para: "Michael Abshoff" <michael.abshoff at googlemail.com>
CC: "'maxima mailing list'" <maxima at math.utexas.edu>
Fecha: lunes, 22 diciembre, 2008 6:40

>>>>> "Michael" == Michael Abshoff
<michael.abshoff at googlemail.com> writes:

    >> I think PARTITION splits EXP into parts, the first which is
    >> independent of VAR.  So I don't know why we need to compute
the sign
    >> of that.

    Michael> Ok, so is this something that you would consider worth fixing?

Yes,  but I need to think a little more about this.  BEHAVIOR needs to
return -1, 0, or 1, so it might have to check the sign.

We'd also have to look at why 5.16.3 doesn't call BEHAVIOR, but 5.17
does.

    Michael> (%i2) forget();
    Michael> (%o2)                                 []
    Michael> (%i3) limit(a*sin(x)/x, x,0);
    Michael> Is  a  positive, negative, or zero?
    Michael> zero;
    Michael> (%o3)                                  a
    Michael> Since I just told Maxima that a equals zero shouldn't
    >> it take that into     Michael> consideration?
    >> Maxima doesn't normally remember your responses to these
questions.
    >> (I kind of like it this way.  It makes exploration easier.)

    Michael> Fair enough.

I think the hgfred routine behaves like you want, but I find that
annoying.

    Michael> And also:
    Michael> (%i4) forget();
    Michael> (%o4)                                 []
    Michael> (%i5) limit(a*sin(x)/x, x,0);
    Michael> Is  a  positive, negative, or zero?
    Michael> Now press CTRL-D and the question is repeated
    >> infinitely:
    Michael> (%i5) limit(a*sin(x)/x, x,0);
    Michael> Is  a  positive, negative, or zero?
    >> That appears to be an issue with Clisp.  In CMUCL, it just prints
out
    >> the prompt again.  Gcl does something similar.
    >> My guess is that Ctrl-D in clisp closes the stream that we're
reading
    >> from and maxima doesn't notice that the stream has been closed
and
    >> keeps asking.  If so, maxima should do something better than that.

    Michael> Ok. I hit CTRL-D by accident in that situation and was
surprised about
    Michael> the seemingly endless loop. It doesn't seem like a high
priority issue
    Michael> from my POV.

I agree.  But maxima ought to be consistent when reasonably possible.

Ray
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