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Matlab

10 years ago
function checkCostFunction(lambda)
%CHECKCOSTFUNCTION Creates a collaborative filering problem
%to check your cost function and gradients
% CHECKCOSTFUNCTION(lambda) Creates a collaborative filering problem
% to check your cost function and gradients, it will output the
% analytical gradients produced by your code and the numerical gradients
% (computed using computeNumericalGradient). These two gradient
% computations should result in very similar values.
% Set lambda
if ~exist('lambda', 'var') || isempty(lambda)
lambda = 0;
end
%% Create small problem
X_t = rand(4, 3);
Theta_t = rand(5, 3);
% Zap out most entries
Y = X_t * Theta_t';
Y(rand(size(Y)) > 0.5) = 0;
R = zeros(size(Y));
R(Y ~= 0) = 1;
%% Run Gradient Checking
X = randn(size(X_t));
Theta = randn(size(Theta_t));
num_users = size(Y, 2);
num_movies = size(Y, 1);
num_features = size(Theta_t, 2);
numgrad = computeNumericalGradient( ...
@(t) cofiCostFunc(t, Y, R, num_users, num_movies, ...
num_features, lambda), [X(:); Theta(:)]);
[cost, grad] = cofiCostFunc([X(:); Theta(:)], Y, R, num_users, ...
num_movies, num_features, lambda);
disp([numgrad grad]);
fprintf(['The above two columns you get should be very similar.\n' ...
'(Left-Your Numerical Gradient, Right-Analytical Gradient)\n\n']);
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