torch.linalg.solve_triangular
torch.linalg.solve_triangular(A, B, *, upper, left=True, unitriangular=False, out=None) -> Tensor
Computes the solution of a triangular system of linear equations
   with a unique solution.
Letting \mathbb{K} be \mathbb{R} or \mathbb{C}, this function
   computes the solution X \in \mathbb{K}^{n \times k} of the linear
   system associated to the triangular matrix A \in \mathbb{K}^{n
   \times n} without zeros on the diagonal (that is, it is invertible)
   and the rectangular matrix , B \in \mathbb{K}^{n \times k}, which
   is defined as
  AX = B

The argument "upper" signals whether A is upper or lower
   triangular.
If "left"= False, this function returns the matrix X \in
   \mathbb{K}^{n \times k} that solves the system
  XA = B\mathrlap{\qquad A \in \mathbb{K}^{k \times k}, B \in
  \mathbb{K}^{n \times k}.}

If "upper"= True (resp. False) just the upper (resp. lower)