Random binary value generation

[TFaiz]

Hello,

I am trying to generate random binary values for each of the grid points in my problem. For example, for grid location (1,1) in a 5x5 grid, I have 24 grid cells as its potential assignee. I want to assign value 1 to 3 random cells, and 0 to the rest of the cells. Can I do that in AMPL?

Thank you.

[Robert Fourer]

There are random functions in AMPL, such as Uniform(i,j) which returns a randomly chosen value between i and j. Using random functions you can write an AMPL script to make random assignments of many kinds. However it's not clear what particular computation you are trying to do, and especially how "grid cells" relate to "grid locations". Can you give a specific example?

(Of course nothing calculated by a computer is truly random, but some care has been taken to make AMPL's random functions return floating-point numbers that compare well to what would be expected of a random sample.)

Bob Fourer
am...@googlegroups.com

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[Tasnim Faiz]

Thank you for your reply.

I have a 5x5 grid with 25 grid cells having coordinates (1,1), (1,2).....(5,4), (5,5).

For (1,1) grid cell, I want to generate random binary (0 or 1) parameter that indicates whether there is a connection between (1,1) and each of the other available 24 cells.

I want to generate random binary parameters B(i,j, x,y)={1,0}
Where (i,j)=(1,1) fixed
And (x,y)=(1,2)....(5,5)
1 indicates (i,j) and (x,y) are connected.
I also want give the limit of the number of connections that (1,1) can have.

Thank you.

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[Robert Fourer]

You could write something like this:

set GRID = {1..5,1..5};
param B {GRID} default 0;
param row; param col;

for {k in 1..3} {
repeat {
let row := ceil(Uniform(0,5));
let col := ceil(Uniform(0,5));
} until not (row = 1 and col = 1) and B[row,col] = 0;
let B[row,col] := 1;
}

Exactly 3 elements of B that are not (1,1) will be assigned the value 1, and the rest will be zero. You can modify this logic as necessary to fit the situation in your model.

Bob Fourer
am...@googlegroups.com

=======

[Tasnim Faiz]

Thank you so much.

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Tasnim Ibn Faiz