Rearranged files & fixed some errors

[SSSayon]

• Files rearranged ▪ commit e1ed5bb

  • Moved (and slightly modified accordingly) environment.yml & README.md from subdirectories of problem-sets-solutions/ to problem-sets/, so that learners can create their virtual environment at the start.
  • Added missing cs229-notes4.pdf back to the syllabus.
  • Removed ps0.pdf in materials/. It was already in problem-sets/.
  • Added supplement materials smo.pdf & smo-paper-platt.pdf to materials/. They are the missing files mentioned by Ng in class notes.

• Typos & errors in PS solutions fixed ▪ commit 3bfc177

  • Added line breaks in three Python Jupiter notebooks where formulas failed to render due to missing line breaks between $$s.

  • In PS3/p04_gmm.py, the log-likelihood was computed incorrectly. Modified

    ll = np.sum(np.log(p_xz))

    to

    ll = np.sum(np.log(np.sum(p_xz, axis=1)))

    The code annotation in fact already gives the right one:

    # By log-likelihood, we mean `ll = sum_x[log(sum_z[p(x|z) * p(z)])]`.

    The incorrect version led to slow convergence in the report (and possibly WRONG convergence value).

  • In PS4/p06_cartpole.py, modified

    if expect_value[0] == expect_value[1]:
        return np.random.randint(2)
    else:
        return np.argmax(expect_value)

    to simply

    return np.argmax(expect_value)

    The incorrect version not only slowed down the speed of the program significantly, but caused the algorithm NEVER CONVERGE under some random seeds, as shown in the report. The randomness is unnecessary and actually fatal.