how to find the maximum of an array in matlab

Question

I have an array with dimensions (517,462,399). I would like to obtain a matrix of size (517,462). Each entry of the matrix (i,j) is the maximum value of the array divided by the sum of the other values. That is, to get the (1,1) entry, we first compare the array entries (1,1,1),(1,1,2)...(1,1,399) and then we divide the maximum value by the sum of the remaining 398 entries.

Did you read the documentation for max and sum?

Daniel
– Daniel

2015-07-07 19:41:18 +00:00
Commented Jul 7, 2015 at 19:41 — Daniel
– Daniel, Commented Jul 7, 2015 at 19:41
yes i did but i could not find how to do it.

mohamed
– mohamed

2015-07-07 19:45:46 +00:00
Commented Jul 7, 2015 at 19:45 — mohamed
– mohamed, Commented Jul 7, 2015 at 19:45

Matt · Accepted Answer · 2015-07-07 20:04:24Z

4

This relatively easy to achieve. Just apply the max and sum functions over the third dimension. The division of the two results has to be made element-wise with the . before the operator.
Here the code:

maxval = max(x,[],3);
result = (sum(x,3)-maxval) ./ maxval;

Note that the max-function needs an empty second argument here, because the third argument indicates the dimension.

edited Jul 7, 2015 at 20:04

answered Jul 7, 2015 at 20:01

Matt

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2 Comments

mohamed Over a year ago

but the sum should exclude the maximum value.

Matt Over a year ago

@mohamed: Just subtract the maximum value before the division. I edited my answer accordingly.

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