On Mon, Dec 19, 2011 at 1:34 AM, Vincent MAILLE <[email protected]> wrote:
> Hello,
>
> I want to eval an expression in R, e.g for E=sqrt(x-1)*sqrt(x-3),
> E.sub(x,0).is_real is true :(
> Is there a way ton force calculus in R sqrt(-1)=nan for exemple ?
>
Only by doing the substitution by hand, I guess. You write your own
function to pull out the sqrt's:
>>> def presub(expr, reps):
... sr = [p for p in expr.atoms(Pow) if p.exp is S.Half]
... for s in sr:
... ssub = s.subs(reps)
... if not ssub.is_real:
... return S.NaN
... return expr.subs(reps)
...
>>> presub(x,{x:0})
0
>>> presub(sqrt(x-1)*sqrt(x-3),{x:0})
nan
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