numpy.log(x, /, out=None, *, where=True, casting='same_kind', order='K', dtype=None, subok=True[, signature, extobj]) = <ufunc 'log'>
Natural logarithm, element-wise.
The natural logarithm log
is the inverse of the exponential function, so that log(exp(x)) = x
. The natural logarithm is logarithm in base e
.
Parameters: |
x : array_like Input value. out : ndarray, None, or tuple of ndarray and None, optional A location into which the result is stored. If provided, it must have a shape that the inputs broadcast to. If not provided or where : array_like, optional Values of True indicate to calculate the ufunc at that position, values of False indicate to leave the value in the output alone. **kwargs For other keyword-only arguments, see the ufunc docs. |
---|---|
Returns: |
y : ndarray The natural logarithm of |
Logarithm is a multivalued function: for each x
there is an infinite number of z
such that exp(z) = x
. The convention is to return the z
whose imaginary part lies in [-pi, pi]
.
For real-valued input data types, log
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, log
is a complex analytical function that has a branch cut [-inf, 0]
and is continuous from above on it. log
handles the floating-point negative zero as an infinitesimal negative number, conforming to the C99 standard.
[R91] | M. Abramowitz and I.A. Stegun, “Handbook of Mathematical Functions”, 10th printing, 1964, pp. 67. http://www.math.sfu.ca/~cbm/aands/ |
[R92] | Wikipedia, “Logarithm”. http://en.wikipedia.org/wiki/Logarithm |
>>> np.log([1, np.e, np.e**2, 0]) array([ 0., 1., 2., -Inf])
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https://docs.scipy.org/doc/numpy-1.14.2/reference/generated/numpy.log.html