P-Median Example Question

Hello, I am trying to code a simple p-median problem. This is what I have so far:

%define data
D = D1; %(896,896) distance matrix
p = 10;

%define variables
x = var(896,896);
y = var(896,1);

%define constraints
F = [sum(y)== p, x <= repmat(y',896,1), sum(x)==1];

%define obj
obj= sum(sum(D.*x));

%solve;default is minimize
solvesdp(F,obj)

But I am getting this error:

Error using horzcat Dimensions of matrices being concatenated are not consistent.

Any suggestions would be appreciated. Thank you.

[Danielle Strong]

Also, the x and y are supposed to be binary. Not sure how to do that.

[Arnab Sen]

x and y are 0 in the script

Answer 1

[Arnab Sen]

Hello Danielle,

I observe the error is coming because of the following statement:

 F = [sum(y)== p, x <= repmat(y',896,1), sum(x)==1];

Here sum(y)== p and sum(x)==1 outputs 1X1 Boolean but x <= repmat(y',896,1) yields Boolean vector of 896X1. The three vector can not be concatenated horizontally due to this dimension mismatch. Modify the aforementioned statement to either one of the following depending on the rest of the code:

F = [sum(y)== p, x <= repmat(y',1,896), sum(x)==1];

or merge them vertically as below:

F = [sum(y)== p; x <= repmat(y',896,1); sum(x)==1];