log1p — computes with accuracy the natural logarithm of its argument added by one
y=log1p(x)
logp1(x)
is the "element-wise" log(1+x) function. y(i,j)=log(1 + x(i,j))
.
This function, defined for x > -1, must be used if we want to compute log(1+x) with
accuracy for |x| << 1.