log function¶
(Shortest import: from brian2 import log)
-
brian2.units.unitsafefunctions.
log
(x[, out])¶ Natural logarithm, element-wise.
The natural logarithm
log()
is the inverse of the exponential function, so thatlog(exp(x)) = x
. The natural logarithm is logarithm in basee
.Parameters: x : array_like
Input value.
Returns: y : ndarray
The natural logarithm of
x
, element-wise.See also
log10()
,log2
,log1p
,emath.log
Notes
Logarithm is a multivalued function: for each
x
there is an infinite number 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. 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,
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.References
[R21] M. Abramowitz and I.A. Stegun, “Handbook of Mathematical Functions”, 10th printing, 1964, pp. 67. http://www.math.sfu.ca/~cbm/aands/ [R22] Wikipedia, “Logarithm”. http://en.wikipedia.org/wiki/Logarithm Examples
>>> np.log([1, np.e, np.e**2, 0]) array([ 0., 1., 2., -Inf])