To put a numerical expression in a+b*%i form, use
block([numer:true],float(rectform(subst([a=1,b=2,...],expr))))
or
ev(float(rectform(expr)),numer,a=1,b=2,...).
These ensures that calculations *within *the rectform are done in
floating-point, not symbolic form, which can be *much* faster that
something like float(rectform(expr)) on large expressions because it avoids
unnecessary intermediate-expression expansion.
Both of these solutions seem unnecessarily complicated. There have been
proposals to treat complex numbers as single numbers, rather than
expressions involving numbers, but as far as I know, no one has
demonstrated a comprehensive solution along those lines (that handles
complex rationals, complex bfloats, etc. uniformly).
You may be wondering what the 'float' is for if we already have numer:true.
That is to catch the edge case where expr is a simple integer: ev(3,numer)
=> 3, not 3.0.
-s
On Sun, Feb 24, 2013 at 10:33 AM, Henry Baker <hbaker1 at pipeline.com> wrote:
> What is the preferred way to convert the results of
> solve(z^3+b*z^2+c*z+d,z), where b,c,d are complex floating point numbers,
> and z is a complex variable, into floating point?
>
> numer doesn't always do it.
>
> expand doesn't always do it.
>
> rectform doesn't always do it.
>
> radcan doesn't do it.
>
> I keep getting expt(...) forms in my display that I can't always get rid
> of.
>
> These are all _constant_ numerical numbers, so there ought to be a way to
> force numerical evaluation.
>
>