# mlclass / exercise-8 / octave / computeNumericalGradient.m

 ``` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29``` ```function numgrad = computeNumericalGradient(J, theta) %COMPUTENUMERICALGRADIENT Computes the gradient using "finite differences" %and gives us a numerical estimate of the gradient. % numgrad = COMPUTENUMERICALGRADIENT(J, theta) computes the numerical % gradient of the function J around theta. Calling y = J(theta) should % return the function value at theta. % Notes: The following code implements numerical gradient checking, and % returns the numerical gradient.It sets numgrad(i) to (a numerical % approximation of) the partial derivative of J with respect to the % i-th input argument, evaluated at theta. (i.e., numgrad(i) should % be the (approximately) the partial derivative of J with respect % to theta(i).) % numgrad = zeros(size(theta)); perturb = zeros(size(theta)); e = 1e-4; for p = 1:numel(theta) % Set perturbation vector perturb(p) = e; loss1 = J(theta - perturb); loss2 = J(theta + perturb); % Compute Numerical Gradient numgrad(p) = (loss2 - loss1) / (2*e); perturb(p) = 0; end end ```