Implement grid search and determine best parameters for C and sigma

ex6/dataset3Params.m

@@ -23,11 +23,38 @@ sigma = 0.3;
 %        mean(double(predictions ~= yval))
 %
 
+grid_search = 0;
 
+if grid_search
+  % Grid search
+  load ex6data3.mat
+  %grid = [0.01, 0.03];
+  grid = [0.01, 0.03, 0.1, 0.3, 1, 3, 10, 30];
+  results = [];
+  for C = grid
+    for sigma = grid
 
+      fprintf('== C = %.2f, sigma = %.2f\n', C, sigma);
+      model= svmTrain(X, y, C, @(x1, x2) gaussianKernel(x1, x2, sigma));
+      predictions = svmPredict(model, Xval);
+      error = mean(double(predictions ~= yval));
+      fprintf('error = %.2f\n\n', error);
 
+      results(end + 1,:) = [C, sigma, error];
 
+    end
+  end
 
+  [_, best_i] = min(results(:,3));
+  C = results(best_i, 1);
+  sigma = results(best_i, 2);
+  error = results(best_i, 3);
+  fprintf('Best: C = %.2f, sigma = %.2f with error = %.2f\n', C, sigma, error);
+else
+  % Found through the grid search above
+  C = 1.00;
+  sigma = 0.10;
+end
 
 % =========================================================================