⇒ when you organize the computation of a neural network, usually you have what's called a forward pass or forward propagation step, followed by a backward pass or what's called a backward propagation step.
⇒ To store an image your computer stores three separate matrices corresponding to the red, green, and blue color channels of this image.
<aside> 💡 And as you implement your neural network later in this course you'll find that a useful convention would be to take the data associated with different training examples, and by data I mean either x or y, or other quantities you see later. But to take the stuff or the data associated with different training examples and to stack them in different columns, like we've done here for both x and y.
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