Miscellaneous tricks and tips

LINUX commands

• fs setacl . system:anyuser read
  allow anyone to read current directory

Matrix calculus

• If A, B, and C are square matrices, then tr ABC = tr BCA = tr CAB.
• ∇_A tr AB = B^T
• ∇_A^T f(A) = (∇_A f(A))^T
• ∇_Atr ABA^TC = CAB + C^TAB^T
• ∇_A|A| = |A|(A^-1)^T if A is a non-singular square matrix.