WignerD.doit doesn't work for half integer spin

[Che Liu]

Hi, 

Seems like WignerD.doit would error for half integer spin.

If you run

with j = 1/2,

then an exception is raised in the doit() function:

The problem rests in the m_values function. For your reference:

Line 56 gives 2.0 for j==1/2, and its is_Integer attribute is false.

The same problem occurs for 

but not for

Any ways to get around it?

My sympy version is 1.6.2, and I run these on a Windows system.

Thanks

[Naman Nimmo]

Hi!

You can pass in a `Rational`.

```

>>> a = WignerD(Rational(1, 2), Rational(1, 2), Rational(1, 2), pi, pi/2, 0)
>>> a.doit()
-sqrt(2)*I/2

```

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[Che Liu]

Thank you for the help!

[Aaron Meurer]

It should probably be made to work with floating point half integers. Half integers are exactly representable as floats, so it isn't an issue.

Aaron Meurer

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