complete and incomplete elliptic integral of first kind
r = delip(x, ck)
real vector/matrix with nonnegative elements
real number between -1 and 1
real or complex number (or vector/matrix) with the same size as
x
The elliptic integral of the first kind with parameter
ck is defined as follow:

Where x is real and positive,
ck is in [-1 1].
If x is less than 1 the result is real.
When called with x a vector/matrix r
is evaluated for each entry of x.