Multiplying two matrices??

[mind-matrix]

delta2 = np.dot(delta3, self.W2.T)*self.sigmoidPrime(self.z2)
This line appears in a function (forward) in the code. Whereby I noticed that z2 was a matrix (per your explanation). I am not that proficient in the python programming language so may not know what it means, but how does np.dot and * differ? The reason I ask this is because I discovered an anomaly in my code while trying to implement this by making a model with inputLayerSize=1, hiddenLayerSize=2 and outputLayerSize=1. Essentially, it should give me predictions for y for the equation y=2x (without knowing the equation firsthand, ofcourse). But when finding delta2 I am stuck because (W2) Transpose is of the order 1 x 2, del3 is of order 1 x 1 and z2 is of the order 1 x 2. How do I matrix multiply del3.W2 and sigmoidPrime(z2) ? (P.S. I was not implementing it in python) and thanks in advance.

[RSKothari]

Hey Kenway, since no has replied back to you yet, I'll try and help.

np.dot is a matrix multiplication while * is an element wise product. So, if you have followed his notes by the line, the final matrix multiplication for djdw1 will be ([3XN]. ([NX2].[2X4]) * [NX4]). I am sorry for not writing the math equation because I don't know how to over here.

He first gets it down to:
[3XN] . [NX4] * [NX4]

Then:
[3XN] . [NX4] = [3X4]

[mind-matrix]

Oh... Ok. Now I see... Thanks.