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Madelon
Madelon

Reputation: 95

How to take power of each element in a matrix in Netlogo?

I would like to take all elements of a matrix to the power of a specific number. I have a matrix using the matrix extension set up like this:

let A matrix:make-constant 4 4 5

which gives a 4x4 matrix with values of 5 in there

Now I want to take all elements in the matrix to the same power, so say I want to take them to power 2, then I want to end up with a 4x4 matrix with numbers 25.

How can I do this?

Upvotes: 2

Views: 580

Answers (1)

Bryan Head
Bryan Head

Reputation: 12580

You can do this a couple ways. The simplest is probably with matrix:times-element-wise. Unfortunately, this will only work for integer powers greater than or equal to 1:

to-report matrix-power [ mat n ]
  repeat n - 1 [
    set mat matrix:times-element-wise mat mat
  ]
  report mat
end

You can also convert the matrix to a list of lists, and then use map on that to raise each element to a power. This has the advantage of working with 0, fractional powers, and negative:

to-report matrix-power [ mat n ]
  report matrix:from-row-list map [ map [ ? ^ n ] ? ] matrix:to-row-list mat
end

map [ ? ^ n ] some-list raises each element of a list to the power of n. matrix:to-row-list converts the matrix to a list of lists. So, we apply map [ ? ^ n ] each list in the result of matrix:to-row-list. Then, we convert the result back into a matrix with matrix:from-row-list.

You can generalize this to do any element-wise operation:

to-report matrix-map [ function mat ]
  report matrix:from-row-list map [ map function ? ] matrix:to-row-list mat
end

Then, we could define the power function as:

to-report matrix-power [ mat n ]
  report matrix-map task [ ? ^ n ] mat
end

Upvotes: 1

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