I forget where this all went last time, but one thing you could do is
not tell students about plot2d and other functions [or redefining
them...]. For example, student_plot2d(F, ...) :=
plot2d(realpart(rectform(F)), ...).
It would be a little more elaborate because plot2d evaluates its
arguments in a non-standard way sometimes.
RJF
Marco Ciampa wrote:
>Sometime ago I've bored all people in this list with a wish espressed by a
>teacher of the high school were I work.
>
>He wanted to restrict the plotting functions only to the real scope of
>numbers (I'm not a mathematician and my knowledge of english is poor so
>please forgive my mistakes, eventually). To extend the concept Maxima could
>be made avare to treat some "base tipes" numbers like integer, natural, rational,
>real or complex (and it could be made extensible too). Such a "typized" CAS would
>resolve automatically the problem of having to plot the result of an
>equation like this:
>
>plot2d([sqrt(x-2) * sqrt(x-4)], [x,-5,5]);
>
>only in the _real_ field.
>
>I suggested the broken hack of tracing the single results for having the
>immaginary part different from zero for plotting. Someone, rightly, argued
>that this way of working is not well defined since one could always add -i*i
>(where i = sqrt(-1)) anywhere in the formula invalidating any part of it.
>
>Well, defining the field of operations from the start could be the answer to
>this point since in the real field the "i" number is not defined so you
>cannot arbitrarly add it in the formula.
>
>This feature will make Maxima the first professional CAS enabled for the more
>wide audience of the high school!
>
>Please be patient, sometimes I do not know what I say! :-)
>
>
>