'Unexpected output' error using SVDS with function handle

I need to pass a function handle, which performs a matrix-vector multiplication, to SVDS. I have

 [U,S,V] = svds( @(x,tflag) denseSparseMatvec(X, 'notransp', B1, B2), [m n], k);

where the output of denseSparseMatvec is m x n and I want the k largest singular values. I get the error

 Unexpected output of function handle with flag 'notransp'. The expected output is a column
 vector of length 20 and of type double.

If, as a test, I simply do M = denseSparseMatvec(X, 'notransp', B1, B2) and then [U,S,V] = svds(M, k), everything works fine.

What's going on here?

Answer 1

[Christine Tobler]

Maybe the problem is that you use both x and X in the definition of the anonymous function? A matrix X in your workspace would be used every time, while the vector x that SVDS passes in is ignored.

Also, the function handle passed to SVDS must compute M*x if the input tflag is 'notransp', and compute M'*x if it is 'transp'.