MATLAB: I’m trying to write a program that calculates the standard deviation of an array without using sum() or std() and I’m having problems

standard deviation program

Here is my code thus far; aberration_waves=[0.213 0.531 0.605 0.448 0.972 0.054 0.889 0.247 0.128 0.711]; N=numel(aberration_waves);
sum_x=0;
for k=aberration_waves
    sum_x=sum_x+k;
end
xavg=sum_x/N;
sum_diff=-xavg;
for x=aberration_waves;
    sum_diff=-xavg+x;
end
std=sqrt((sum_diff^2)/(N-1));
I have no problem with finding the average it's the standard deviation that is vexing me. Specifically sum_diff, it's not what it should be, I would appreciate some help

Best Answer

hi, try :
 aberration_waves=[0.213 0.531 0.605 0.448 0.972 0.054 0.889 0.247 0.128 0.711];   
 N=numel(aberration_waves);
 sum_x=0;
 for k=aberration_waves
    sum_x=sum_x+k;
 end
 xavg=sum_x/N;
 % STD
 S=0;
 for k=1:N
  S=S+(aberration_waves(k)-xavg).^2;
 end
 VARIANCE=S/(N-1);
 STD=sqrt(VARIANCE);
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