User defined functions for standard deviation

Hi. I'm trying to come up with a function that calculates the standard deviation of an array. I understand there's a built in function that does this but I'm not allowed to use it for my class.

Here's what I have so far,I seem to have hit a wall and would really appreciate any help or suggestions.

Thanks!!! :)

x = [1 2 3 4];
sum = 0;
k = length(x);
for i = 1: k
    sum = sum+x(i);
    mean = (sum)/k;
    stdev = ((x(i)-mean).^2);
    stdev = sqrt((stdev)/k);
end

[Walter Roberson]

Naming a variable "sum" is going to lead to problems. Same with "mean".

Answer 1

[Azzi Abdelmalek]

sum and mean are built-in functions, use instead for example som and moy.

You should use two for loop, the first to calculate the mean of x, and the second to calculate the std of x. Note that the Matlab function std calculate

sqrt(sum((xi-mean(x))^2/(n-1)))   % n is the length of x