Fix broken Matrix::transpose()
Due to a confusion between the number of lines N and the number of columns M, Matrix::transpose() gave wrong results for matrices with N != M.
This also adds a testcase demonstrating the problem to matrixtest.cc.
Due to a confusion between the number of lines N and the number of columns M, Matrix::transpose() gave wrong results for matrices with N != M.
This also adds a testcase demonstrating the problem to matrixtest.cc.