Nonsimplifying nounforms: abs, realpart, carg, etc. (maxima-Bugs-902290)

                                    
________________________________________________________________________
> Von:macrakis at gmail.com [mailto:macrakis at gmail.com] Im Auftrag von
> Stavros Macrakis
> Gesendet: Sonntag, 11. Januar 2009 19:54
> An: maxima at math.utexas.edu
> Cc: Dieter Kaiser
> Betreff: Nonsimplifying nounforms: abs, realpart, carg, etc.
> (maxima-Bugs-902290)



> The bug is that some nounforms, like realpart(1), do not simplify.

To have this simplification we need a function which can be called by
the simplifier. I think we have the following options:

1. Implement a simplifying function like sin, cos, ...

   Evaluation and simplification is done by a function which
   is called only by the simplifer. No VERB function is needed.

   The decision is: Should the functions for the complex components 
   including realpart and imagpart be simplifying functions or not.

   The next question is: Can we use a call to trisplit to get a 
   simplified expressions. What should be improved e.g.
   'realpart(z+w) --> realpart(z+w) and not realpart(z)+realpart(w)?

2. Implement VERB/NOUN concept like diff, integrate, ...
   
   Implement both functions: The VERB function is called by the Maxima 
   user. The NOUN function again is called only by the simplifier and
   supports some elementary simplifications e.g. like 'diff(x,x)--> 1 
   or 'integrate(0,x) --> 0.

   The decision is: What code should be duplicated for the simplifier
   function e.g. 'realpart(x) --> x for all symbols not declared to be 
   complex and real numbers. Should complex numbers also be included 
   like 'realpart(x+%i*y) --> x ?

3. Do nothing   

   In this case 'realpart(1) --> realpart(1) is not a bug. A 
   simplification is not supported.

Dieter Kaiser