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Homework Help: Stochastic Gradient Descent

  1. Mar 4, 2014 #1
    1. The problem statement, all variables and given/known data

    Suppose I wish to fit a plane
    [tex] z = w_1 + w_2x +w_3y [/tex]
    to a data set [tex] (x_1,y_1,z_1), ... ,(x_n,y_n,z_n) [/tex]

    Using gradient descent

    2. Relevant equations


    3. The attempt at a solution

    I'm basically trying to figure out the 3-dimensional version of the example on wiki.
    The objective function to e minimized is:

    [tex] Q(w) = \sum_{i = 1}^n Q_i(w) = \sum_{i = 1}^n (w_1 + w_2x_i + w_3y_i - z_i)^2 [/tex]
    I want to find the parameters of [tex]w_1,w_2,w_3 [/tex]

    The iterative method updates the parameters [tex]w^{(0)}_1,w^{(0)}_2,w^{(0)}_3 [/tex]
    1-step in the iteration
    \left( \begin{array}{ccc}
    w^{(1)}_1 \\
    w^{(1)}_3 \end{array} \right) = \left( \begin{array}{ccc}
    w^{(0)}_1 \\
    w^{(0)}_2 \\
    w^{(0)}_3 \end{array} \right) + \alpha \times \left( \begin{array}{ccc}
    2(w^{(0)}_1 + w^{(0)}_2x_i + w^{(0)}_3 y_i - z_i) \\
    2x_i(w^{(0)}_1 + w^{(0)}_2x_i + w^{(0)}_3 y_i - z_i) \\
    2y_i(w^{(0)}_1+ w^{(0)}_2x_i + w^{(0)}_3 y_i - z_i) \end{array} \right) [/tex]

    [tex]\alpha [\tex] is the step size.
    Last edited: Mar 5, 2014
  2. jcsd
  3. Mar 8, 2014 #2
    Looks good. Whats your question?
  4. Mar 8, 2014 #3
    Just wanted to make sure that I didn't cheat or something in my solution. When I run it in c++ it works very well.
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