How to write a for loop that saves every 100th value?

I have a code that has a for loop that calculates the eccentricity of an orbit as time passes, and I need to plot the results. Saving every single value of accentricity would be very large task, so I need to save every 100th value of eccentricity, along with the corresponding time, to some type of file.

This is what I have so far but it very much doesn't work, any advce would be greatly appreciated.

    m = 0;
for i = 1: m
    m = m + 1;
    if m == 100
        C{i} = emag;
                    C2{i} = t;
                    E(i,1) = emag;
                    E(i,2) = t;
                    matrixToWrite = [t emag];
                    writematrix(matrixToWrite, 'myData.txt')
                    m = 0;

                    t = t + delta;


    end   
end

[Rik]

Please don't post duplicate questions. If someone is already helping you, posting a second question with the same content is a waste of time.

[Lauren Miller]

I thought it would be more helpful reworded and the code posted is slightly different. I apologise if this has bothered you, i was unaware of the rules

[Rik]

In general you can do that by editing the question instead of posting a new one.

[Lauren Miller]

Thanks for your advice :)

Answer 1

[Scott MacKenzie]

If I understand your quesiton correctly, a for-loop is not necessary. It seems you have an array emag with many values and a corresponding array t with the timestamp for each value. Here's some code (using mock arrays) that saves every 100th value in t and emag in a file mydata.txt:

emag = rand(1,23456);
t = rand(1,23456);

n = length(emag);

emag100 = emag(1:100:n);
t100 = t(1:100:n);

writematrix([emag100' t100'], 'mydata.txt');

[Lauren Miller]

Thank you!!

Answer 2

[EmirBeg]

First of all you set m=0 and then start a loop from 1 to m. So i guess your loop does nothing.

You need to set a new variable for the amount of iterations your loop will go through. After that you should also set m to 0 again in your If-statement so you get a value every 100th iteration and not just the 100th.

[EmirBeg]

I realise that you already added the m=0 in your If-statement or i was blind and didn't see it.

This should still be changed:

m = 0;
t = 5000; %amount of times you go through the loop
for i = 1: t
    m = m + 1;
    if m == 100
%...
    end
    end

[Lauren Miller]

Thank you so much that's really helpful!