索引超过了 MATLAB 中的数组元素数 (9)

Question

So I am getting an error where I believe n1 is larger than the array after n becomes n = 3, which is giving the error in ma. Premise of the code is to take 1 2, 3 4 5, 6 7 8 9, etc. and average each group. Pretty sure I have to change the length but not sure how to go about it. What should I do? Here is the code:

clear all
mdata = [1 2 3 4 5 6 7 8 9];
n1 = 1;
k = 1;
for n = 1:length(mdata)
    ma(n) = (1/(k + 1)) * sum(mdata(n1:n1 + k));
    n1 = ((n1 + k) + 1);
    k = k + 1;
    std_ma = std(mdata);
end

Error message:

Index exceeds the number of array elements (9).

Error in untitled22 (line 11) ma(n) = (1/(k + 1)) * sum(mdata(n1:n1 + k));

Answer 1

The issue is that you are replacing the value of n1 with n1+k+1 on each step through the loop. At the start of the 4th iteration, n1=10 and k=4 , meaning you are trying to take the sum of elements 10:14 but the array only has 9 elements.

It is not clear from your question exactly what averages you are trying to calculate through all of the iterations of the loop and so it is difficulty to say more. But, most likely, you do not need to manually calculate the average yourself. Just define the subset of the data you want to work with on that iteration and take the mean of that.

I am also guessing that you want to modify the assignment of std_ma at the end of your loop to only perform the std on the subset of data you are working with. Currently you are doing the calculation over all values in mdata and repeating that same calculation 9 times.