Plotting a variable as a function of the iteration number in a for loop

Hi,

Basically I have loop, within which is a 12X12 array of zeros and ones. For each cycle of the loop I need to sum the value of the array(which I am able to do) and then plot this value against the iteration/loop number.

Obviously the value of the array changes for each loop so I am a bit stuck as to how to plot the graph.

Eg. Do I output the values for each loop to a seperate new array/file, which I then draw upon at the end of the loop to create the graph? Or is there some way to construct a graph in stages as the program loops-essentially holding the plot figure and adding new points to the existing plot for each iteration.

Any help would be very much appreciated! If I have not explained very well just let me know and I can try and explain further/provide code snippets.

Thanks in advance,

Mike Scott

[Oleg Komarov]

Is the loop unavoidable?

Answer 1

[Matt Fig]

Here is an example. Note that if your loop index is 1-to-N, then you won't need the loop counter and this can be simplified in obvious ways. I do have to wonder, however, if you can avoid the loop altogether. Only a look at your code can shed light here...

lp_idx = 10:.5:30;  % This is the loop index.
S = zeros(1,length(lp_idx));  % Pre-allocation.
cnt = 1;  % Loop counter.

for ii = lp_idx
   t = magic(ii);  % An array which changes in loop
   S(cnt) = sum(t(:)); % The sum of each array
   cnt = cnt + 1;  % Increment the counter.
end

plot(lp_idx,S)  % Plot sum vs. loop index
xlabel('Loop Index')
ylabel('Matrix Sum')

[Mike Scott]

%

% This is where I should type my 'help facily'. Everything types here

% before the executable command lines will be displayed when the user types

% help gameoflife into the command window.

clear all

clc

A = [0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 1 1 1 1 1 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 1 1 1 1 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 1 1 1 1 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0];

B = [0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 1 1 1 1 1 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 1 0 0 0 0 0 0;0 0 0 0 1 0 0 0 0 0 0 0;0 0 0 1 0 0 0 0 0 0 0 0;0 0 1 0 0 0 0 0 0 0 0 0;0 1 0 0 0 0 0 0 0 0 0 0;0 0 0 0 0 0 0 0 0 0 0 0];

mycolmap=[1 1 1;0.5 0.5 0.5]; %Define color map

colormap(mycolmap)%set matlab's colour matrix equal to mycolmap

done = 0;

while (done ~= 1)

start = input('Enter the desired starting condition, 1 or 2: ');

if(start == 1)

disp(['You have selected choice ' num2str(start)])

done = 1;

image(0.5, 0.5, A(2:11, 2:11)+1)%display starting condition A(+1 is because...)

C = A;

elseif(start == 2)

disp(['You have selected choice ' num2str(start)])

done = 1;

image(0.5, 0.5, B(2:11, 2:11)+1)%display starting condition B(+1 is because...)

C = B;

else

disp('Starting condition not recognised. Please re-select');

end

end

T=zeros(12,12);% create a 12X12 grid of zeros, for next iteration

title('Game of life')

grid on

% axis([0 10 0 10])

'linewidth';2;

pause(1)

iter = input('Enter the number of iterations you wish to observe: '); %This allows the user to select the number of iterations they wish the game of life program to carry out

%iter=1,pause,iteration;

fps = input('Enter the delay between each frame(in seconds) you would like to view the generation in: ');

for n=1:iter %This carries out the game of life rules a set number of times as decided by the user.

for i=2:11;

for j=2:11;

C(i,j); %selects each element of the matrix individually

G=C(i-1:i+1,j-1:j+1);%creates a 3X3 matrix around each element of the original matrix

S(i,j)=sum(sum(G))-C(i,j); %Sums the elements of the 3X3 grid minus the centre element value to give the number of neighbours

%disp('Number of alive cells: ')

% This next section applies the Game of Life rules, using the summed

% values for neighbours for each element in the original matrix.

if (C(i,j)==1) && (S(i,j)==2)||(S(i,j)==3);

T(i,j)=1;

elseif (C(i,j)==0 && S(i,j)==3);

T(i,j)=1;

elseif (C(i,j)==1 && (S(i,j)==0)||(S(i,j)==1));

T(i,j)=0;

else (C(i,j)==1 && (S(i,j)>=4));

T(i,j)=0;

end

end

end

image(0.5, 0.5,T(2:11, 2:11)+1);%displays next iteration of life on a new matrix

title(['Game of life. Generation number: ' num2str(n)]);

grid on

axis([0 10 0 10])

alive=sum(sum(T));

disp(['Generation number: ' num2str(n)]); %displays the corresponding generation number as the figure of the generation evolves

disp(['Number of alive cells: ' num2str(alive)]);

C=T;

%K(i,j)=sum(sum(T));

pause(fps)%delay between each frame(iteration), as defined by user

end

figure(2);hold; % This brings up a new figure(the active figure)or uses figure 2, which the plot will be stored in and hence will not overwrite the figure displaying the game of life. Hold-opens the figure for multiple plots

plot(n,alive);

I thought I'd best just put the whole program. I have had to create a game of life program that visualises the generation of cells using some rules. The part I am concerned with now is the plotting of the number of alive cells (given by alive=T..) against the loop/iteration number.

You can see the value for T is generated within each loop but the actually plot command is outside the loop.

Hope this makes some kind of sense to you?

Thanks in advance,

Mike

[Mike Scott]

The last section of the code is the relevant part, the rest is just if you needed a greater understanding of the program itself.

Mike

[Matt Fig]

So just before your loop, put this:

alive = zeros(1,iter);

Then in the loop:

alive(n)=sum(T(:));

and to plot:

plot(1:n,alive);

[Matt Fig]

Note that sum(T(:)) is preferred over sum(sum(T)).

[Mike Scott]

Wow I have been reading through so many topics without any luck. That's great, thanks so much for your response Matt.

Much appreciated,

Mike

Answer 2

[vega valentine]

don't you just have to plot it outside the loop? I think what you need to do is just store every values you needed in every loop into a separate array/variable, and then after the looping is done, you can plot that array/variable.

[Mike Scott]

Yes, the plot command is written outside of the loop. You have cleared up my query regarding whether to store the values as the program loops into a seperate array, which makes sense now. Is there a command that I should use to set up this array and then assign the values generated in each loop to?

Thanks for your reply

[Oleg Komarov]

Post the code you're using, formatting with the code button.