Plotting the variance. Please help fix my code

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Duncan Smith
Duncan Smith 2011-3-27
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

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回答（1 个）

Oleg Komarov
Oleg Komarov 2011-3-27
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);

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