function B = rowswap(A,i,j)
    % ROWSWAP   Given an m x n matrix A and two intergers i and j
    %           between 1 and m, this function produces an m x n matrix
    %           that results from intercharging row i and row j of A.
    B = A;
    B(i,:) = A(j,:);
    B(j,:) = A(i,:);