Hello all > -----Original Message----- > From: [EMAIL PROTECTED] [mailto:numpy- > [EMAIL PROTECTED] On Behalf Of David Grant > Sent: 16 August 2006 17:11 > To: Discussion of Numerical Python > Subject: Re: [Numpy-discussion] some work on arpack > > > > On 8/16/06, Keith Goodman <[EMAIL PROTECTED]> wrote: > > On 8/15/06, David Grant <[EMAIL PROTECTED]> wrote: > > > My idea is (if I have time) to write an eigs-like function in > python > > that will only perform a subset of what Matlab's eigs does for. It > > will, for example, compute a certain number of eigenvalues and > > eigenvectors for a real, sparse, symmetric matrix (the case I'm > > interested in) > > Will it also work for a real, dense, symmetric matrix? That's the > case > I'm interested in. But even if it doesn't, your work is great news > for > numpy. > > Real, dense, symmetric, well doesn't scipy already have something for > this? I'm honestly not sure on the arpack side of things, I thought arpack > was only useful (over other tools) for sparse matrices, I could be wrong.
Maybe SciPy can also do this, but what makes ARPACK useful is that it can get you a few eigenvalues and eigenvectors of a massive matrix without having to have the whole thing in memory. Instead, you provide ARPACK with a function that does A*x on your matrix. ARPACK passes a few x's to your function and a few eigenvalues and eigenvectors fall out. I recently used MATLAB's eigs to do exactly this. I had a dense matrix A with dimensions m x n, where m >> n. I wanted the eigenvalues of A'A (which has dimensions m x m, which is too large to keep in memory). But I could keep A and A' in memory I could quickly calculate A'A*x, which is what ARPACK needs. Cheers, Albert ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Numpy-discussion mailing list Numpy-discussion@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/numpy-discussion
