numpy.log1p(x, /, out=None, *, where=True, casting='same_kind', order='K', dtype=None, subok=True[, signature, extobj]) = <ufunc 'log1p'>
Return the natural logarithm of one plus the input array, elementwise.
Calculates log(1 + x)
.
Parameters: 


Returns: 

For realvalued input, log1p
is accurate also for x
so small that 1 + x == 1
in floatingpoint accuracy.
Logarithm is a multivalued function: for each x
there is an infinite number of z
such that exp(z) = 1 + x
. The convention is to return the z
whose imaginary part lies in [pi, pi]
.
For realvalued input data types, log1p
always returns real output. For each value that cannot be expressed as a real number or infinity, it yields nan
and sets the invalid
floating point error flag.
For complexvalued input, log1p
is a complex analytical function that has a branch cut [inf, 1]
and is continuous from above on it. log1p
handles the floatingpoint negative zero as an infinitesimal negative number, conforming to the C99 standard.
[1]  M. Abramowitz and I.A. Stegun, “Handbook of Mathematical Functions”, 10th printing, 1964, pp. 67. http://www.math.sfu.ca/~cbm/aands/ 
[2]  Wikipedia, “Logarithm”. https://en.wikipedia.org/wiki/Logarithm 
>>> np.log1p(1e99) 1e99 >>> np.log(1 + 1e99) 0.0
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https://docs.scipy.org/doc/numpy1.17.0/reference/generated/numpy.log1p.html