Plotting the variance. Please help fix my code

Hi all, I currently have a graph of a trace which shows great fluctuations. Therefore, i would like to plot the variance of this trace using a defined window length. The initial trace is a plot of coordinates against force. The coordinates along the x-axis go from 0 to 300 and there are 73500 points. Therefore i would like to plot the variance of the force for xcoordinates 0 to 1000, plot this, calculate the variance from 1000 to 2000, plot this and so on until the end.

My code so far is

function[X1,Y1,X2,Y2,c,c1]=SMPcomparison(points1,points2,day)

 fname1 = points1; % relates the user inputted file to the variable fname(n)
  fname2 = points2;
  points1=load (points1); % loads the matrix associated with user inputted variable into the workspace
  points2 = load(points2);
X1 = points1(:,1);% takes respective column of matrix and correlates this with either an X or Y coordinate
Y1 = points1(:,2);
X2 = points2(:,1);
Y2 = points2(:,2); 

subplot(1,1,1),plot(X1,Y1,'g',X2,Y2,'r') % plots data sets 
N=length(X1);

    x=1
    y=1
    i = 1;
  j=1000;
 n= length(Y1);
  while i<n-1000
      for c = i:1000:n
             v = var(Y1(i:j))
          i = i+1000;
          j=i+1000
           variance{y,2} = v
         y=y+1;
                             if j>=n-1000;
              break
         %end
      %end
      %record the data to an output matrix
% subplot(2,1,2),plot(X1 ,v)

end

Answer 1

[Oleg Komarov]

You can use this approach:

% Supose you have an array of 73500 elements and you want to calculate the 
% variance on non overlapping windows of 1000 elements
A = rand(73500,1);

% I leave out the last 500 elements
B = A(1:end-mod(numel(A),1000));

% Reshape B into 1000 by 73 and calculate the variance on the 73 windows
Out = var(reshape(B,1000,numel(B)/1000),2);