mok-kong shen <mok-kong.shen at t-online.de> writes:
> Hello,
>
> This is a newbee's problem: I just tried wxMaxima 0.8.4 and entered as
> in the manual (chap. 1, Introduction to Maxima) the following command:
>
> plot2d(sin(x)/x,[x,-20,20])
>
> I obtained the plot but on ending the plot window there appeared a
> message in the main window:
>
> plot2d: expression evaluates to non-numeric value somewhere in
> plotting range.
>
> What had I done wrongly? Thanks for your help in advance.
What happened is that Maxima tried to evaluate sin(x)/x at x=0, getting
0/0, which doesn't make sense as a number. To check that's what's
happening, you can perturb one of the interval ends very slightly so
that you won't end up evaluating at zero:
(%i1) plot2d( sin(x)/x, [x,-20,20] );
plot2d: expression evaluates to non-numeric value somewhere in plotting range.
(%o1)
(%i2) plot2d( sin(x)/x, [x,-20,20.001] );
(%o2)
(%i3)
But, as you can see from the plot, Maxima and gnuplot are robust enough
to ignore this problem and just not plot the point at all. Since there
are lots of samples, you can't see the difference.
Rupert
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