numpy.log#

numpy.log(x,/,out=None,*,where=True,casting='same_kind',order='K',dtype=None,subok=True[,signature])=<ufunc'log'>#

Natural logarithm, element-wise.

The natural logarithmlog is the inverse of the exponential function,so thatlog(exp(x)) = x. The natural logarithm is logarithm in basee.

Parameters:
xarray_like

Input value.

outndarray, None, or tuple of ndarray and None, optional

A location into which the result is stored. If provided, it must havea shape that the inputs broadcast to. If not provided or None,a freshly-allocated array is returned. A tuple (possible only as akeyword argument) must have length equal to the number of outputs.

wherearray_like, optional

This condition is broadcast over the input. At locations where thecondition is True, theout array will be set to the ufunc result.Elsewhere, theout array will retain its original value.Note that if an uninitializedout array is created via the defaultout=None, locations within it where the condition is False willremain uninitialized.

**kwargs

For other keyword-only arguments, see theufunc docs.

Returns:
yndarray

The natural logarithm ofx, element-wise.This is a scalar ifx is a scalar.

Notes

Logarithm is a multivalued function: for eachx there is an infinitenumber ofz such thatexp(z) = x. The convention is to return thez whose imaginary part lies in(-pi, pi].

For real-valued input data types,log always returns real output. Foreach value that cannot be expressed as a real number or infinity, ityieldsnan and sets theinvalid floating point error flag.

For complex-valued input,log is a complex analytical function thathas a branch cut[-inf, 0] and is continuous from above on it.loghandles the floating-point negative zero as an infinitesimal negativenumber, conforming to the C99 standard.

In the cases where the input has a negative real part and a very smallnegative complex part (approaching 0), the result is so close to-pithat it evaluates to exactly-pi.

References

[1]

M. Abramowitz and I.A. Stegun, “Handbook of Mathematical Functions”,10th printing, 1964, pp. 67.https://personal.math.ubc.ca/~cbm/aands/page_67.htm

[2]

Wikipedia, “Logarithm”.https://en.wikipedia.org/wiki/Logarithm

Examples

>>>importnumpyasnp>>>np.log([1,np.e,np.e**2,0])array([  0.,   1.,   2., -inf])
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