What is this for loop doing since numfires equals one and what is actually happening inside the loop with this line "C(fires(i​,1),fires(​i,2))=2;"?

 function y = fire_sim(N,p)
     figure(1);
     %sets size of forest NxN
     C = ones(N,N);
     Z = zeros(N,N);
     x = 1:N;
     y = 1:N;
     %Set initial fire
     fires = [floor(N/2),floor(N/2)];
     [numfires,temp] = size(fires);
     for i = 1:numfires
         C(fires(i,1),fires(i,2))=2;
     end
     %Simulate spread
     maxsteps = 1000; %number of iterations to plot
     k=0;
     while k<maxsteps && numfires>0
         lastC = C;
         numfires_next = 0;
         fires_next = [];
         for i = 1:numfires
             if fires(i,1)~=1
                 if C(fires(i,1)-1,fires(i,2))==1
                     r = rand(1);
                     if r < p
                         numfires_next = numfires_next + 1;
                         C(fires(i,1)-1,fires(i,2))=2;
                         fires_next(numfires_next,:)=[fires(i,1)-1,fires(i,2)];
                     end
                 end
             end
             if fires(i,1)~=N
                 if C(fires(i,1)+1,fires(i,2))==1
                     r = rand(1);
                     if r < p
                         numfires_next = numfires_next + 1;
                         C(fires(i,1)+1,fires(i,2))=2;
                         fires_next(numfires_next,:)=[fires(i,1)+1,fires(i,2)];
                     end
                 end
             end
             if fires(i,2)~=1
                 if C(fires(i,1),fires(i,2)-1)==1
                     r = rand(1);
                     if r < p
                         numfires_next = numfires_next + 1;
                         C(fires(i,1),fires(i,2)-1)=2;
                         fires_next(numfires_next,:)=[fires(i,1),fires(i,2)-1];
                     end
                 end
             end
             if fires(i,2)~=N
                 if C(fires(i,1),fires(i,2)+1)==1
                     r = rand(1);
                     if r < p
                         numfires_next = numfires_next + 1;
                         C(fires(i,1),fires(i,2)+1)=2;
                         fires_next(numfires_next,:)=[fires(i,1),fires(i,2)+1];
                     end
                 end
             end
             C(fires(i,1),fires(i,2))=0;
         end
         surf(x,y,C,C);
         view(360,90);
         colormap([0 0 0; 0 1 0; 1 0 0])
         caxis([0 2]);
         axis([1,length(x),1,length(y),0,2])
         shading interp
         title(sprintf('Step = %.0f',k))
         drawnow;
         k=k+1;
         if sum(sum(abs(lastC-C)))==0
              break
         end
         fires = fires_next;
         numfires = numfires_next;
     end

Answer 1

[Image Analyst]

There are very few comments, for which the author should be embarrassed and ashamed of themselves.

It looks like fires is an array of row, column indexes where it's on fire. A value of C equal to 1 means original, unburnt forest. Since they set an initial fire in the center of the C array, if C is 2, the element is on fire. So I'm guessing that if C = 0, there was a fire there but now the fire has been put out or burned out at that element.

I don't know why you'd need both the fires array and the C array. I'd think the C array alone would be enough to keep track of the status (original, on fire, burnt out) of the location, but whatever - as long as it works.

[Image Analyst]

By the way, you might find this related blog entry fun: http://blogs.mathworks.com/graphics/2015/03/16/how-the-tiger-got-its-stripes/?s_tid=srchtitle