[Maxima] Ordering of vector variables?
sen1 at math.msu.edu
Mon Mar 24 12:15:42 CDT 2008
Robert Dodier wrote:
> On Mon, Mar 24, 2008 at 9:45 AM, Raymond Toy (RT/EUS)
> <raymond.toy at ericsson.com> wrote:
>> While playing with donlp2, I noticed that maxima orders vector variables
>> in "reverse" order. For example,
>> sum(x[k],k,1,5) -> x+x+x+x+x.
>> While I usually just accept whatever order maxima wants to display
>> variables, this particular example seems wrong. There's a natural
>> ordering and it's by the index of the variable.
>> Any reason why it should be in reverse order? Any objections to
>> changing it for this case? (I don't know if that's really possible or
>> not. I haven't looked.)
> The terms x, x, ... are stored in order of increasing index.
> Whether they are displayed that way or reversed is controlled
> by the global variable powerdisp. When powerdisp=true the terms
> are displayed in order of increasing index.
> I'm not opposed to changing the default value of powerdisp to true.
> Aside from changing powerdisp, we could also change GREAT
> (the function which implements Maxima's idea of canonical
> ordering). Changing GREAT could have rippling effects, though.
> Robert Dodier
> Maxima mailing list
> Maxima at math.utexas.edu
For those of us who already have routines which make use of the current
ordering of variables, e.g. as in
%i1) p: x^2 + y^2 - x*y;
(%o1) y - x y + x
changing some defaults would create havoc and, perhaps, cause a lot more
time spent modifying existing debugged code.
If it is only a matter of setting a flag to be 'true' or 'false' in new
code, why not leave the defaults as they are?
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