Plotting a matrix in a for loop.

Hello community,

I'm new to Matlab and having trouble figuring out how to plot a matrix.

I made a transition matrix that is a markov chain, and I'm given a state vector. Im supposed to perform 31 steps of the markov chain, and on a single figure plot the probability of being in each state at a given iteration. My data is this so far:

SEI = [0.7 0.4 0 0.2 0 0; 0.3 0 0 0 0 0; 0 0.3 0 0 0 0; 0 0.3 1 0.8 0 0; 0 0 0 0 0.25 0; 0 0 0 0 0.75 1];

x0 = [1;0;0;0;0;0];

for i = 1:31

xk =(SEI^i)*x0;

end

where "xk" would be the resulting probability at each step. How do I plot this inside the for loop?

Answer 1

[ME]

You have a couple of options here. One is that you store all of the steps of the Markov chain during the for loop and then plot them afterwards - something like this:

SEI = [0.7 0.4 0 0.2 0 0; 0.3 0 0 0 0 0; 0 0.3 0 0 0 0; 0 0.3 1 0.8 0 0; 0 0 0 0 0.25 0; 0 0 0 0 0.75 1];
x0 = [1;0;0;0;0;0];
for i = 1:31
xk(i) =(SEI^i)*x0;
end
plot([1:31],xk(:))

or alternatively, if you have to plot inside the for loop then you can do this as

SEI = [0.7 0.4 0 0.2 0 0; 0.3 0 0 0 0 0; 0 0.3 0 0 0 0; 0 0.3 1 0.8 0 0; 0 0 0 0 0.25 0; 0 0 0 0 0.75 1];
x0 = [1;0;0;0;0;0];
figure; hold on;
for i = 1:31
xk =(SEI^i)*x0;
plot(i,xk,'.b');
end

I'm having a bit of a blank as to how you could get those points to join up into a single line but if the dots (or other symbol of your choosing) will do then this should work.

Answer 2

[Bob Thompson]

With MATLAB you don't really want to perform the plot inside the loop in this case. Just save your results in a matrix and plot once afterwards.

for i = 1:31
xk(i) =(SEI^i)*x0; % Index the results to an element of a matrix
end
plot((1:31),xk)

[ME]

Can't believe how similar our answers are and how closely timed either!