expint not functioning as expected?

Hi all,

I am trying to use expint in a routine I am coding, however it doesn't seem to be working as I expect it to. I expect it to function as shown by the link below

http://mathworld.wolfram.com/ExponentialIntegral.html

With the output starting negative then becoming positive around 0.372. Have I misunderstood what this function does?

I am using the command below to check output:

>> plot(expint(0:0.01:1.5))

Thanks,

J

Answer 1

[Matt Fig]

I think perhaps you are looking for this:

Ei = @(x)real(-expint(-x));
x = -2:0.001:3;
plot(x,Ei(x))

[J]

So effectively I was just assuming to see the real part of the answer? Just me being stupid again then...

[Matt Fig]

You probably confused one definition of the exponential integral for the other. Read the doc for EXPINT carefully.