Return the natural logarithm of one plus the input array, element-wise.
Calculates log(1 + x).
Parameters:x : array_like
Returns:Input values.
y : ndarray
Natural logarithm of 1 + x, element-wise.
Notes
For real-valued input, log1p is accurate also for x so small that 1 + x == 1 in floating-point 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 real-valued 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 complex-valued input, log1p is a complex analytical function that has a branch cut [-inf, -1] and is continuous from above on it. log1p handles the floating-point negative zero as an infinitesimal negative number, conforming to the C99 standard.
References
Examples
>>> np.log1p(1e-99) 1e-99 >>> np.log(1 + 1e-99) 0.0
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