Program exercise
- Feedforward and cost function
- complete the code in nnCostFunction.m
- costFunction is
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- The input Matrix X is a 5000 * 400 matrix， and the output vector y is 5000 * 1.
- The initial theta provided by assignment is a vetor and need to be urolled into matrix. This procedure can be done by using the function reshape(X, M, N). This function return a M*N matrix whose element is clockwise of vector X. An error is returned if X does not have M*N element. And, we can use theta1 directly because the code have reshape the matrix for us.
- when I calculate the transform_y, I made I stupid mistake ...
- another mistake , forget to remove theta1 when do the regulization cost funtion. And forget how to trim a matrix
