Join Probability Distribution is defined as below after knowing the Conditional Probability# \(p(y_k|x_j)\) and \(p(x_j)\):
$$ p(x_j, y_k) = p(y_k|x_j) p(x_j) $$
To find \(p(y_k, x_j)\), we can just transpose the matrix so that the first row of \(p(x_j, y_k)\) becomes the first column of \(p(y_k, x_j)\), the second row becomes the second column and so on.