#10087: bug with fast_float, imag and sqrt : NotANumber isn't fine.
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Reporter: fmaltey | Owner: burcin
Type: defect | Status: new
Priority: major | Milestone:
Component: symbolics | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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I'm looking at the float result of y by fast_float for m=0.0 :
{{{
var('m')
y=imag(sqrt(1+sqrt(m-1)))
fast_float (y, m)(0) # I get nan
}}}
Now I try the constant function (without m),
the value must be the previous one for m=0.
{{{
z=imag(sqrt(1+sqrt(-1)))
fast_float(z,m)(0) # I get the right 0.45...=2^(1/4)*sin(pi/8)
}}}
I feel (but I can't prove) that this bug is near from the #7165 bug I
found in parametric_plot [that maybe calls fast_float in this case].
When I read the y.imag() value, there is at the end a fuzzy
{{{...*sqrt(abs(sqrt(m-1)+1))}}}
This {{{sqrt(m-1)}}} is Not_A_Number if m=0 because fast_float only uses
real numbers. So this call might be replaced by an other expression, with
real part and imaginary part.
There is no expression as {{{sqrt(1+sqrt(-1))}}} in {{{z.imag()}}} and
Sage runs right.
F.
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Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10087>
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