What is CNTK dynamic axis?


CNTK has static and dynamic axis. Static axis remains the same throughout the whole life cycle of the model. Dynamic axis has the following characteristics :-

a) varies from instance to instance
b) typically unknown
c) maybe ordered.

Sounds like a minibatch


Taken directly from Microsoft website :-

To make this more concrete, let’s consider two examples. First, let’s see how a minibatch of short video clips is represented in CNTK. Suppose that the video clips are all 640x480 in resolution and they are shot in color which is typically encoded with three channels. This means that our minibatch has three static axes of length 640, 480, and 3 respectively. It also has two dynamic axes: the length of the video and the minibatch axis. So a minibatch of 16 videos each of which is 240 frames long would be represented as a 16 x 240 x 3 x 640 x 480 tensor.

Dynamic axis in this case are video length (240 frames) and a total of 16 videos.


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