2D convolution in matlab

Question

function C = convolve_slow(A,B)
(file name is accordingly convolve_slow.m ) 
This routine performs convolution between an image A and a mask B.
Input: A - a grayscale image (values in [0,255]) 
 B - a grayscale image (values in [0,255]) serves as a mask in the convolution. 
Output: C - a grayscale image (values in [0,255]) - the output of the convolution. 
 C is the same size as A.
Method: Convolve A with mask B using zero padding. Assume the origin of B is at 
 floor(size(B)/2)+1. 
 Do NOT use matlab convolution routines (conv,conv2,filter2 etc). 
 Make the routine as efficient as possible: Restrict usage of for loops which 
 are expensive (use matrix multiplications and matlab routines such as dot etc). <br>
 To simplify and reduce ifs, you should pad the image with zeros before starting your convolution loop. 
 Do not assume the size of A nor B (B might actually be larger than A sometimes).

here is my solution for this exercise. please elaborate on any change you have done or suggesting since i'm new to matlab and image processing.

function [ C ] = convolve_slow( A,B )<br>
%This routine performs convolution between an image A and a mask B.
%
% Input: A - a grayscale image (values in [0,255]) 
% B - a grayscale image (values in [0,255]) serves as a mask in the convolution.
% Output: C - a grayscale image (values in [0,255]) - the output of the convolution. 
% C is the same size as A.
% 
% Method: Convolve A with mask B using zero padding. Assume the origin of B is at floor(size(B)/2)+1. 
% init C to size A with zeros
C = zeros(size(A));
% make b xy-reflection and vector
vectB = reshape(flipdim(flipdim(B,1),2)' ,[] , 1);
% padding A with zeros
paddedA = padarray(A, [floor(size(B,1)/2) floor(size(B,2)/2)]);
% Loop over A matrix:
for i = 1:size(A,1)
 for j = 1:size(A,2)
 startAi = i;
 finishAi = i + size(B,1) - 1;
 startAj = j;
 finishAj = j + size(B,2) - 1;
 vectPaddedA = reshape(paddedA(startAi :finishAi,startAj:finishAj)',1,[]);
 C(i,j) = vectPaddedA* vectB;
 end
end
end 

Answer 1

Rather than making four variables just to index the matrix, I would go for two in such a way:

paddedA(i :i_end,j:j_end)