How to save every iteration of for loop and plot

I am attempting to find how long it takes to reach a specific spot in an image. This spot will change based on 'fractionofdisc'. The column index 'n(k)' will tell me how many steps it takes to get to that specific point on the image. This code, however, only spits out 1 value for x and n instead of supplying every value as the for loop iterates. I need help understanding why this might be happening. As an update, it does seem as if the code runs one iteration at x = 0.1 and stops. I would like to know what the code is doing from x = 0.1 to x = 1.0.

fractionofdisc = 0.1:0.1:1.0;

y = uint8(double(mean(mean(raw_image)))*5); % changing data type may not be necessary
Mp2 = raw_image > y;
sum_Mp2 = sum(Mp2);
sum_sum_Mp2 = sum(sum_Mp2);

x = zeros(length(fractionofdisc));
n = zeros(length(fractionofdisc));

    for k = 1:length(fractionofdisc)
        n(k) = 0; % n must be a variable so it holds information for each iteration
        cumsum = 0;
    
        % While loop needed to sweep across the x values until it reaches
        % cumsum
        x(k) = fractionofdisc(k);
        while cumsum < x*sum_sum_Mp2
            n(k) = n(k) + 1;      % column index
            cumsum = cumsum + sum_Mp2(n(k));
        end
    end
    
    
figure(2)
plot(x,n,'-g')
xlabel('Fraction of Disc')
ylabel('Column Index')

Answer 1

[Akihumi]

What is your numerical range of raw_image? If it is between 0 and 1, all elements of Mp2 will be 0, thus the while loop

while cumsum < x*sum_sum_Mp2
    n(k) = n(k) + 1;      % column index
    cumsum = cumsum + sum_Mp2(n(k));
end

will never be executed, since x*sum_sum_Mp2 = 0.

[Steven Manz]

I have attached the image, and the code for you to see. But you are correct. Mp2 is 2048 x 2048 logical array with ones and zeros. How can I fix this? Do I need to make Mp2 a double? So you are aware as well, sum_Mp2 is a 1x2048 double, and sum_sum_Mp2 is single value that is class double.

[Akihumi]

% This line sets a threshold that has the value of 5 times of the average of all pixel values
y = uint8(double(mean(mean(raw_image)))*5); % changing data type may not be necessary

% This line labels a zero if the pixel doesn't exceed the threshold, 
% otherwise labels a one if it exceeds the threshold
% So the output will always be zeros and ones
Mp2 = raw_image > y;

% This line computes the sum of the columns,
% i.e. the number of pixels that exceed the threshold in one column
sum_Mp2 = sum(Mp2);

% This line computes the total number of pixels that exceed the threshold
sum_sum_Mp2 = sum(sum_Mp2);

I'm nor very sure what is the intention of the following for loop and while loop. Do you want to run through the columns and add up the cumsum with corresponding sum_Mp2 until the cumsum is larger than corresponding fractionofdisc*sum_sum_Mp2?

Note that x is actually also a 1x10 vector that is [0.1,0,0,0...,0] in the first iteration of for loop k, and it'll be [0.1,0.2,0,0,0,...,0] in the 2nd iteration. And for now your while loop condition x*sum_sum_Mp2 will output a 1x10 vector that has trailing zeros in the iterations smaller than k==10. Is that what you wanted?