Try to be as explicit as possible:
specify the full path to tezos-client
specify the absolute directory containing the data, especially the aliases (generally --base-dir /home/[..USER..]/.tezos-client)
If it does not work, copy-paste the error messages, so that we can understand the problem.
You have to do it manually... Here's one approach for compute log(x) assuming you are representing x as a fraction
find integer m through binary search such that 2^m <= x < 2^(m+1) (m may be negative)
let m' = m + (1 if |x/2^(m+1)-1| < |x/2^m-1| else 0) (the closests of m or m+1)
let x' = x / 2^m', note that |x'-1| < 1/3 and log(x) = log(2^m' x'...
I have a contract for binary log that uses few multiplications and can be adjusted for any fixed point precision: https://github.com/Sophia-Gold/michelson/blob/master/log2fix.tz. I don't think it can be written in SmartPy because last I checked it lacks shifts. Depending on your needs you could use this with change of base or Arthur's method.
As explained by Arvidj, there are no floating point numbers in Michelson (or SmartPy), no exp or log function.
While working with natural numbers, you can implement by hand some examples which may or may not be enough for you. Some examples here: