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numpy.log1p(x[, out]) =
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Return the natural logarithm of one plus the input array, element-wise.
Calculates
log(1 + x)
.Parameters: x : array_like
Input values.
Returns: y : ndarray
Natural logarithm of
1 + x
, element-wise.Notes
For real-valued input,
log1p
is accurate also forx
so small that1 + x == 1
in floating-point accuracy.Logarithm is a multivalued function: for each
x
there is an infinite number ofz
such thatexp(z) = 1 + x
. The convention is to return thez
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 yieldsnan
and sets theinvalid
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
[R48] M. Abramowitz and I.A. Stegun, ?Handbook of Mathematical Functions?, 10th printing, 1964, pp. 67. http://www.math.sfu.ca/~cbm/aands/ [R49] Wikipedia, ?Logarithm?. http://en.wikipedia.org/wiki/Logarithm Examples
>>> np.log1p(1e-99) 1e-99 >>> np.log(1 + 1e-99) 0.0
numpy.log1p()
2017-01-10 18:14:53
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