K()

function out=K(W)

Input:

• W: $\prod S \times N_s$ matrix containing initial guess for eigensolutions

Global variables:

• gbl_G2: Square magnitude of G vectors

Output:

• out: Preconditioner 1/(1+G2) applied to each column of W

Implement in the file ``K.m'' the preconditioner function of the above prototype.
Hint: Your code should closely resemble that for Linv().