# [Maxima] I need advice on how to use radcan

Stavros Macrakis macrakis at alum.mit.edu
Mon Aug 30 10:08:58 CDT 2010

Barton,

I think that you want radexpand:false in your examples below.  Otherwise the
general simplifier has already changed sqrt(x^2)=>abs(x) before radcan even
sees it.  With radexpand:false, the two cases both give results without the
'abs'.

-s

On Sun, Aug 29, 2010 at 10:14, Barton Willis <willisb at unk.edu> wrote:

> -----maxima-bounces at math.utexas.edu wrote: -----
>
>
> >The introduction of abs() in the answers to radcan makes a hash of its attempt to make algebraic sense.
>
> Example:
>
>  (%i1) radcan(sqrt(a^2)), domain : real, radexpand : true;
>  (%o1) abs(a)
>
>  (%i2) radcan(sqrt(a^2-2*a*b+b^2)), domain : real, radexpand : true;
>  (%o2) b-a
>
> The outputs %o1 and %o2 are inconsistent, I think. My Macsyma 2.2 gives
> abs(b-a) for %o2
> and abs(a) for %o1, by the way.
>
> The user documentation for radcan should be improved. Something like:
>
>  For any n-variable Maxima expression e, the equation radcan(e) = e is an
> identity on some
>  nonempty open subset D of C^n. The set D might differ from what you would
> like it to be.
>
> --Barton
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