How do I get the sum of the averages for a specific time step?

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Nesha Wright 2018-6-29

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回答： Nesha Wright 2018-7-4

I am using: mean_time = sum(mean(mean(mean(total)))); to get the sum of the averages of a 4D matrix. How do I change this to get the sum for a specific timestep? For example, if I wanted timestep 5 or 8 specifically rather than the sum of the entire thing (which is what the above does).

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Adam Danz 2018-6-29

编辑：Adam Danz 2018-6-29

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In which of the 4 dimensions are the time steps?

When you calculate mean(total) you are taking the mean across the first dimension. So when you calculate mean(mean(total)), you are calculating the first dimension of the mean(total) array. To demonstrate that, see how the size of each dimension changes after each mean:

K>> size(total)
ans =
     4     4     4     4
K>> size(mean(total))
ans =
     1     4     4     4
K>> size(mean(mean(total)))
ans =
     1     1     4     4
K>> size(mean(mean(mean(total))))
ans =
     1     1     1     4

If you were to use squeeze() in each of the steps above you'd see the number of dimensions decrease at each step.

If you want to take the mean over a dimension other than the first, use the second input to mean(). To answer your question, it depends upon which dimension describes the time steps.

Nesha Wright 2018-6-29

The time steps are the 4th dimension. So if I want the sum average of the last timestep (# 588) I would use squeeze(sum(mean(mean(mean(total))))? How do I limit it to just the 588th time step?

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