Rewrite the full pi constant as acos(-1.)

[eldritchconundrum]

No description provided.

[laurentlb]

Do you expect users to put exactly the same number of PI digits as you?

[eldritchconundrum]

Yes. If they don't put as many digits as what fits in a double, it becomes semantically hazardous to replace the number by a different number.

[laurentlb]

What if they put more digits?
If that's the maximum precision of float, it should also match right? If that's the case, please add a test.