Implement a Matlab function that produces the Gaussian pyramid of an image:

function G_pyramid = CV_G_pyramid(I, k, sigma)
%
% CV_G_pyramid - Gaussian pyramid image
% On input:
%     I (mxn array): input image
%     k (int): size of window (2k+1 by 2k+1 window)
%     sigma (float): sigma for Gaussian function (scale parameter)
% On output:
%     G_pyramid (mxnxp array): p images (stored in upper left corner) comprising Gaussian pyramid
% Call:
%     pyr = CV_G_pyramid(I,4,2);    % does a 9x9 window
% Method:
%     See Forsyth and Ponce, Chapter 7
% Author:
%     Your name
%     UU
%     Fall 2012
%