Why is airy(3,1) complex? (No numerical round-off in the complex part)

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Why does Matlab return a complex number for airy(3,1)?
The result is a pure real, the imaginary part is identically zero (no numerical round off), yet the value is considered complex?
>> format long
>> y = airy(3,1)
y =
0.932435933392775
>> isreal(y)
ans =
0
>> format hex
>> imag(y)
ans =
0000000000000000

Answers (3)

Wayne King
Wayne King on 18 Sep 2012
Edited: Wayne King on 18 Sep 2012
What release are you using?
>> format long
>> isreal(airy(3,1))
ans =
1

David Wilson
David Wilson on 18 Sep 2012
R2012a
  2 Comments
Wayne King
Wayne King on 18 Sep 2012
I've confirmed that behavior in R2012a, but it is fixed in R2012b, let me check the bug reports
Wayne King
Wayne King on 18 Sep 2012
I don't see it as a bug report David, but the behavior is fixed in 12b, airy(3,1) returns the scalar with attribute real

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Matt Tearle
Matt Tearle on 18 Sep 2012
Looks like a bug in 12a. If you do
whos y
it shows the class as double (complex), so isreal is working properly, but how the heck it gets a complex y with 0 real part is a mystery to me. It looks like the problem is actually coming from besselmx, which airy calls:
z = besselmx(real('B'),1,1)
whos z
It's fixed in 12b, where airy is now a built-in.

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