Help with Matlab code

Hi everyone!

I am looking at a matlab code which I need help in understanding. Itt is set up in a matrix form, but I have difficulty understanding the full function it represents.

Static variables:

MS1 = eye(16,16); %system for {p,p*,mc,mc*,l,l*,y,y*,yh,yh*,yf,yf*,rk,rk*,r,r*}

Dynamic:

MD1 = eye(26); %system for x={ph,ph*,pf,pf*,w,w*,c,c*,i,i*,e,k,k*,b,r_,r*_,ph_,ph*_,pf_,pf*_,w_,w*_,e_,a,a*,psi} 
MD2 = zeros(26,26); %MD1*x_{t+1} = MD2*x_{t}+MD3*epsilon_{t+1}
MD3 = zeros(26,5); %epsilon={em,em*,ea,ea*,epsi} - current {em,em*}, but future {ea,ea*,epsi}!

This code snippet below is an example from the dynamic part which I struggle to understand. I have the paper without the exact functions. So based on this I am trying to understand and set up a function from it.

I would highly appreciate it if someone could help me understand what it means. For instance MD2(7,:): I am not sure what ":" means.

MD1(7,7) = sigma; %c
MD1(7,:) = MD1(7,:)+MS(1,:);
MD2(7,7) = sigma; 
MD2(7,:) = MD2(7,:)+MS(1,:)+MS(15,:);
MD3(7,:) = MSin(15,:);

Answer 1

[Image Analyst]

The colon, :, means "all" so

MD2(7,:) = MD2(7,:)+MS(1,:)+MS(15,:);

means set all columns in row 7 of MD2 to be what they originally were (that's MD2(7,:)) PLUS the sum of all columns in rows 1 and 15 of MS added together (that's the MS(1,:)+MS(15,:) part).

So in other words, to do in a for loop instead of vectorized:

for col = 1 : size(MD2, 2)
    MD2(7, col) = MD2(7, col) + MS(1,col) + MS(15, col);
end

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[Molly]

Thank you so much, I was just watching a few concepts with practical questions, but I will jump straight to the one you sent me now. And give an update on my work.

Thank you!