Two variable Cumulative Sum calculation

As you were interested, I've attached a function which I just wrote that computes the cumulative 2d sum using for loops. I did a little bit of testing to compare run times (using tic,toc) for a large array (10^4 x 10^4) using this double loop compared to the one line B = cumsum(cumsum(A,1),2). It seemed that it took almost twice as long using the double loop.

function B = cumsum2d(A)
%CUMSUM2D Compute cumulative sum over 2d array
%   B = cumsum2d(A) computes 2-d matrix B whose elements are
%       the cumulative sum over elements of 2-d matrix A
%       such that B(i,j) is the sum of all elements of A whose row and
%       column indices are less than or equal to i and j respectively
% get the total number of rows and columns, we need these for end condition
% on loops
[numRows,numCols] = size(A);
% preallocate matrix the same size as A to hold result
B = zeros(numRows,numCols);
% loop through rows and columns accumulating totals
for jCol = 1:numCols
    % initialize cumulative sum of elements in this column
    sumThisCol = 0;
    for iRow = 1:numRows
        % update the sum of elements in the current column
        sumThisCol = sumThisCol + A(iRow,jCol);
        
        % update the cumulative sum of all of the elements to the left and
        % above this element (inclusive)
        % (need branch to handle special case of first column since there
        % isn't anything to the left of that)
        if jCol > 1
            % in the interior, there is a column to the left of this one
            B(iRow,jCol) = B(iRow,jCol - 1) + sumThisCol;
        else
            % this is the first column, there is nothing to the left of it
            % to add
            B(iRow,jCol) = sumThisCol;
        end
    end
end