Find max/min eigenvalue of a symmetric matrix

I know I can use eig() to find all eigenvalues as well as eigenvectors and then use max/min to find the max/min eigenvalues. However, that method is not efficient given a big matrix. 
I heard of Lanczos algorithm that allows to find extreme eigenvalues. 
I wonder if there is any function in matlab that can find max/min eigenvalues quickly?
BTW, I consider symmetric positive semi-definite matrices if that makes problem any easier. 

Thanks,

Answer 1

[Andrei Bobrov]

please read: doc eigs

[Khanh]

Thank you, Andrei. I wonder if it's the fastest function for calculating min/max eigenvalues available on matlab? It's quite slow when the size of matrix is more than 1,000 by 1,000, though.

Answer 2

[Andrew Knyazev]

try http://www.mathworks.com/matlabcentral/fileexchange/48-lobpcg-m