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It’s mentioned in the video but not really explained, can someone explain to me why that happens

Hi @rmwkwok Raymond,

I think you had replied to this doubt recently. Probably you can direct to the same post.

Regards

DP

It’s because in a partial derivative, each weight is considered separately, and all the other weights are considered as constants.

Since the partial derivative of a constant is zero, all the other “non-j” terms become zeros, so they evaporate from the equation for each w_j.