how to approximate exponential integral

I was doing an iterating algorithm on a chi-square distribution. I want to get a numerical result but instead matlab gave me the following expression:

y =
 
9.488080697552181667109694795787 - (ei(-1/2)*exp(1/2))/2

Is there a way I can tell matlab to give a numerical approximation? Thanks!

Answer 1

[John D'Errico]

vpa(y)

or

double(y)

Either will suffice, depending on whether you want a symbolic floating point number of not.

[Shunhao Huang]

It works! Thank you!