[SOLVED] Extract upper or lower triangular part of a numpy matrix

Issue

I have a matrix A and I want 2 matrices U and L such that U contains the upper triangular elements of A (all elements above and not including diagonal) and similarly for L(all elements below and not including diagonal). Is there a numpy method to do this?

e.g

A = array([[ 4.,  9., -3.],
           [ 2.,  4., -2.],
           [-2., -3.,  7.]])

U = array([[ 0.,  9., -3.],
           [ 0.,  0., -2.],
           [ 0.,  0.,  0.]])

L = array([[ 0.,  0.,  0.],
           [ 2.,  0.,  0.],
           [-2., -3.,  0.]])

Solution

Try numpy.triu (triangle-upper) and numpy.tril (triangle-lower).

Answered By – mathematical.coffee

Answer Checked By – Jay B. (BugsFixing Admin)