Exercise:Softmax Regression
From Ufldl
(→Step 2: Implement softmaxCost) |
(→Step 2: Implement softmaxCost) |
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It is important to vectorize your code so that it runs quickly. We also provide several implementation tips below: | It is important to vectorize your code so that it runs quickly. We also provide several implementation tips below: | ||
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| + | Note: In the provided starter code, <tt>theta</tt> is a matrix where each the ''j<sup>th</sup> row'' is <math>\theta_j</math> | ||
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'''Implementation Tip''': Computing the ground truth matrix - In your code, you may need to compute the ground truth matrix <tt>M</tt>, such that <tt>M(r, c)</tt> is 1 if <math>y^{(c)} = r</math> and 0 otherwise. This can be done quickly, without a loop, using the MATLAB functions <tt>sparse</tt> and <tt>full</tt>. <tt>sparse(r, c, v)</tt> creates a sparse matrix such that <tt>M(r(i), c(i)) = v(i)</tt> for all i. That is, the vectors <tt>r</tt> and <tt>c</tt> give the position of the elements whose values we wish to set, and <tt>v</tt> the corresponding values of the elements. Running <tt>full</tt> on a sparse matrix gives the full representation of the matrix for use. Note that the code for using <tt>sparse</tt> and <tt>full</tt> to compute the ground truth matrix has already been included in softmaxCost.m. | '''Implementation Tip''': Computing the ground truth matrix - In your code, you may need to compute the ground truth matrix <tt>M</tt>, such that <tt>M(r, c)</tt> is 1 if <math>y^{(c)} = r</math> and 0 otherwise. This can be done quickly, without a loop, using the MATLAB functions <tt>sparse</tt> and <tt>full</tt>. <tt>sparse(r, c, v)</tt> creates a sparse matrix such that <tt>M(r(i), c(i)) = v(i)</tt> for all i. That is, the vectors <tt>r</tt> and <tt>c</tt> give the position of the elements whose values we wish to set, and <tt>v</tt> the corresponding values of the elements. Running <tt>full</tt> on a sparse matrix gives the full representation of the matrix for use. Note that the code for using <tt>sparse</tt> and <tt>full</tt> to compute the ground truth matrix has already been included in softmaxCost.m. | ||
