ValueError math domain error

Question

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 NR2method py   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

User · Answer

you are getting math domain error for either one of the reason   either you are trying to use a negative number inside log function or a zero value

User · Answer

You are trying to do a logarithm of something that is not positive   Logarithms figure out the base after being given a number and the power it was raised to  log 0  means that something raised to the power of 2 is 0  An exponent can never result in 0   which means that log 0  has no answer  thus throwing the math domain error   Note  0 0 can result in 0  but can also result in 1 at the same time  This problem is heavily argued over

User · Answer

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    gt  gt  gt  from math import log  gt  gt  gt  log -1  Traceback  most recent call last     File   lt pyshell 59 gt    line 1  in  lt module gt      log -1  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

User · Answer

You may also use math log1p    According to the official documentation        math log1p x        Return the natural logarithm of 1 x  base e   The result   is calculated in a way which is accurate for x near zero    You may convert back to the original value using math expm1 which returns e raised to the power x  minus 1

[python] ValueError: math domain error

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