# How to use matrix in workspace in a script

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John on 4 Jan 2013
Hi,
I have have the function below saved in a script.
The matrix P is defined in the function.
How could I refer to a matrix P in the workspace instead? It is a 200x200 matrix so I can't type it into the function.
Thank you
function [X] = DTMC_SimulationOne(n)
%This is the vector that will hold the entire realization of the chain.
%For example, X(1) is the initial state (1 in our case), X(2) is the second
%state of the chain, etc.
X = zeros([n+1,1]);
%This is the transition matrix of my imaginary chain. Your transition
%mattrix is different.
P = [ 1/3 2/3 0;
1/4 1/2 1/4;
1 0 0];
%Set the initial condition. The first state is told to be state 1.
X(1) = 1;
%The main FOR LOOP. It runs from 1 through n, and updates the state based
%upon the previous state.
for j = 1:n
%Generate a uniform random variable.
r = rand;
if r < P(X(j),1)
X(j+1) = 1;
elseif r < P(X(j),1) + P(X(j),2)
X(j+1) = 2;
else
X(j+1) = 3;
end
end

Walter Roberson on 4 Jan 2013
function [X] = DTMC_SimulationOne(n, P)
if nargin < 2
P = [ 1/3 2/3 0;
1/4 1/2 1/4;
1 0 0];
end

Image Analyst on 4 Jan 2013
You need to return P in the output argument list:
function [P X] = DTMC_SimulationOne(n)
if you want to refer to it in the workspace of the calling routine. Then you "refer" to is like you do any matrix:
theValueOfAnElementOfP = P(row, column);
Of course P is already able to be referred to in the workspace of the function DTMC_SimulationOne. You do know that there are different workspaces, don't you? Each function has its own local workspace.