Moving course1 to course1 subdir.

machine_learning/course1/mlclass-ex4-008/mlclass-ex4/checkNNGradients.m

@@ -0,0 +1,52 @@
+function checkNNGradients(lambda)
+%CHECKNNGRADIENTS Creates a small neural network to check the
+%backpropagation gradients
+%   CHECKNNGRADIENTS(lambda) Creates a small neural network to check the
+%   backpropagation gradients, it will output the analytical gradients
+%   produced by your backprop code and the numerical gradients (computed
+%   using computeNumericalGradient). These two gradient computations should
+%   result in very similar values.
+%
+
+if ~exist('lambda', 'var') || isempty(lambda)
+    lambda = 0;
+end
+
+input_layer_size = 3;
+hidden_layer_size = 5;
+num_labels = 3;
+m = 5;
+
+% We generate some 'random' test data
+Theta1 = debugInitializeWeights(hidden_layer_size, input_layer_size);
+Theta2 = debugInitializeWeights(num_labels, hidden_layer_size);
+% Reusing debugInitializeWeights to generate X
+X  = debugInitializeWeights(m, input_layer_size - 1);
+y  = 1 + mod(1:m, num_labels)';
+
+% Unroll parameters
+nn_params = [Theta1(:) ; Theta2(:)];
+
+% Short hand for cost function
+costFunc = @(p) nnCostFunction(p, input_layer_size, hidden_layer_size, ...
+                               num_labels, X, y, lambda);
+
+[cost, grad] = costFunc(nn_params);
+numgrad = computeNumericalGradient(costFunc, nn_params);
+
+% Visually examine the two gradient computations.  The two columns
+% you get should be very similar. 
+disp([numgrad grad]);
+fprintf(['The above two columns you get should be very similar.\n' ...
+         '(Left-Your Numerical Gradient, Right-Analytical Gradient)\n\n']);
+
+% Evaluate the norm of the difference between two solutions.  
+% If you have a correct implementation, and assuming you used EPSILON = 0.0001 
+% in computeNumericalGradient.m, then diff below should be less than 1e-9
+diff = norm(numgrad-grad)/norm(numgrad+grad);
+
+fprintf(['If your backpropagation implementation is correct, then \n' ...
+         'the relative difference will be small (less than 1e-9). \n' ...
+         '\nRelative Difference: %g\n'], diff);
+
+end