Tue May 20 22:25:36 2025

python_mistake_test():
  python version: 3.10.12
  numpy version:  1.26.4
  Demonstrate some python mistakes.

python_mistake01():
  Show that A=B is not the right way to copy arrays.

  Use "=" to copy an array

  a =                         [ 1.  2.  3.  4.  5.  6.  7.  8.  9. 10.]
  (Bad) b = a =               [ 1.  2.  3.  4.  5.  6.  7.  8.  9. 10.]
  Do stuff to b, but do not touch a...
  a =                         [-1. -1. -1. -1.  1.  1.  1.  1.  1.  1.]
  b =                         [-1. -1. -1. -1.  1.  1.  1.  1.  1.  1.]

  Repeat, but use COPY rather than "="

  a =                         [ 1.  2.  3.  4.  5.  6.  7.  8.  9. 10.]
  (Correct) b = a.copy() =    [ 1.  2.  3.  4.  5.  6.  7.  8.  9. 10.]
  Do stuff to b, but do not touch a...
  a =                         [ 1.  2.  3.  4.  5.  6.  7.  8.  9. 10.]
  b =                         [-1. -1. -1. -1.  1.  1.  1.  1.  1.  1.]

python_mistake02():
  QR factorization on array stored as integer or real values.
  User software fails for integer values.

  A = np.array ( [ [1,2,3],[4,5,6],[7,8,10]]).
  Algorithm     norm(Q^T*Q-I)    norm(Q*R-A)
   mgs_vector    1.732051e+00     1.743560e+01
   np.linalg.qr  5.235557e-16     5.528866e-15

  A = np.array ( [ [1.0,2.0,3.0],[4.0,5.0,6.0],[7.0,8.0,10.0]]).
  Algorithm     norm(Q^T*Q-I)    norm(Q*R-A)
   mgs_vector    3.529601e-15     0.000000e+00
   np.linalg.qr  5.235557e-16     5.528866e-15

python_mistake_test():
  Normal end of execution.
Tue May 20 22:25:37 2025