ValueError: math domain error

I was just testing an example from Numerical Methods in Engineering with Python.

    from numpy import zeros, array
    from math import sin, log
    from newtonRaphson2 import *

    def f(x):
        f = zeros(len(x))
        f[0] = sin(x[0]) + x[1]**2 + log(x[2]) - 7.0
        f[1] = 3.0*x[0] + 2.0**x[1] - x[2]**3 + 1.0
        f[2] = x[0] + x[1] + x[2] -5.0
        return f

    x = array([1.0, 1.0, 1.0])
    print newtonRaphson2(f,x)

When I run it, it shows the following error:

    File "example", line 8, in f
        f[0] = sin(x[0]) + x[1]**2 + log(x[2]) - 7.0
    ValueError: math domain error

I have narrowed it down to the log as when I remove log and add a different function, it works. I assume it is because of some sort of interference with the base, I can't figure out how. Can anyone suggest a solution?

Your code is doing a log of a number that is less than or equal to zero. That's mathematically undefined, so Python's log function raises an exception. Here's an example:

    >>> from math import log
    >>> log(-1)
    Traceback (most recent call last):
      File "<pyshell#59>", line 1, in <module>
    ValueError: math domain error

Without knowing what your newtonRaphson2 function does, I'm not sure I can guess where the invalid x[2] value is coming from, but hopefully this will lead you on the right track.