Return the natural logarithm of one plus the input array,
element-wise. Calculates log(1 + x). x : array_like y : ndarray
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. |[R46]||M.
Abramowitz and I.A. Stegun, “Handbook of Mathematical
Functions”, 10th printing, 1964, pp. 67.
http://www.math.sfu.ca/~cbm/aands/| |[R47]||Wikipedia, “Loga