user2954167 - 1 year ago 227
Python Question

# How to take the ln of a function in python?

I used polyfit to find a fitline of a data set, but now I need to find the natural log of that fitline function and plot it. Here's what I have so far:

``````#Fit line for PD
deg = 10
zn = np.polyfit(l_bins, l_hits, deg)
l_pn = np.poly1d(zn)
pylab.plot(l_bins, l_pn(l_bins), '-g')
ln_list = []
for all in l_bins:
ln_list.append(np.log(l_pn(all)))
pylab.plot(l_bins, ln_list, '-b')
``````

Is there a better or more correct way to do this?

Edit
I would suggest using `numpy.log` as Roger Fan demonstrated below. Since you are already using numpy arrays, this will certainly outperform using `map` or a list comprehension.

If you have a `list` of z-values, you can use `map` to perform some function to each value, in this case `log` (which is `ln`).

``````>>> x = range(1,10)
>>> x
[1, 2, 3, 4, 5, 6, 7, 8, 9]

>>> from math import log
>>> map(log, x)
[0.0, 0.6931471805599453, 1.0986122886681098, 1.3862943611198906, 1.6094379124341003, 1.791759469228055, 1.9459101490553132, 2.0794415416798357, 2.1972245773362196]
``````

You could use any function, so you may use `numpy.log` if you prefer.

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