On Fri, Sep 15, 2006 at 10:26:21AM -0600, Robert Dodier wrote:
> On 9/13/06, Robert Dodier <robert.dodier at gmail.com> wrote:
>
> > Maxima 5.9.3.99rc4 (Maxima 5.10.0 release candidate 4)
> > is available to download the SF file manager,
> > http://sourceforge.net/project/showfiles.php?group_id=4933
>
> So far (2 days) no new errors have been reported for rc4.
> If no new errors are reported by 9/20, I'll tag rc4 as 5.10.0.
> Maybe someone can test rc4 over the weekend.
>
Please document this plot variable:
On Thu, Apr 20, 2006 at 05:43:35PM -0700, Andrej Vodopivec wrote:
> I have just commited the patch to CVS. plot_realpart is true by
> default. Please test it.
>
> Andrej
>
> On 3/24/06, Andrej Vodopivec <andrej.vodopivec at gmail.com> wrote:
> > > i think i am in favor of this. it should be maintained by
> > > set_plot_option (i.e., not a global flag). how is this going to work,
> > > exactly?
> >
> > I have attached a patch for plot.lisp which implements this. As you
> > can see the adaptive plotter has to be modified too (for efficiency
> > reasons).
> >
> > Use it like
> >
> > plot2d(log(sin(x)), [x,-6,6]);
> > plot2d(log(sin(x)), [x,-6,6], [plot_realpart, false]);
> >
> > (I haven't tested it much though).
> >
> > Andrej
And someone just showed me that this method is't good enough.
If you do a plot of like this
plot2d([sqrt(x-2) * sqrt(x-4)], [x,-5,5]);
you get a graph with a positive and a negative part. The positive is ok
since the function is defined for values x>=4 but the negative part (for
x<=2) is't defined since the product reset the 2 imaginary components but
the function is't defined for the 2 sqrt.
The solution (but I do not know how to apply it to maxima) is to calculate
the value of result_imaginary variable for every part of the equation.
When the calc is started result_imaginary is set to 0.
Whatever part of the function creates a complex number this variable must be
set to 1 to flag that the equation is _not_ defined even if the imaginary part
is zeroed before the end of the calc.
Perhaps this go too deep into maxima to make it into this version but this
behaviour of the plot_realpart variable IMHO _must_ be documented!
PS: Maple do the same plot error :-)
Thank you again,
--
Marco Ciampa
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