Question

I have this code that throws a math domain error exception:

v = -1.0

for i in range (201):
    print acos (v)
    v += 0.01

But if I change it to this, it works:

v = -100

for i in range (201):
    print acos (v / 100.0)
    v += 1

Is this because of rounding?

How to best solve this in Python? Or should I just do it like my last example?

Answer 1

If you do:

>>> format(0.01, '.30f')
'0.010000000000000000208166817117'

you can see that 0.01 (as a floating point number with double precision) is bigger than the number 0.01 you learned at school.

So, when you sum it 100 times, the error gets bigger:

>>> sum([0.01]*100)
1.0000000000000007

And that’s enough to give a math domain error.

What can you do?

• Use the second code
• round() it to less decimal points:

.

>>> round(1.0000000000000007, 13)
1.0

13 or 14 may be enough.