Computes the exponential weighted integral function for real arguments. The expei
function takes only a single argument
y = expei(x)
where x is either a float or double array. The output
vector y is the same size (and type) as x.
The expei function is defined by the integral:
Here is a plot of the expei function over the range [-5,5].
--> x = linspace(-5,5);
--> y = expei(x);
--> plot(x,y); xlabel('x'); ylabel('expei(x)');
which results in the following plot.