Smooth vector data with a specific step

I need to smooth the data, but the smooth function flips the response of the data, which makes things a little more difficult

x = rand(1,4097);
y = rand(1,4097);
z1=smooth(x(1:10),x(1:10),0.8,'rloess')'; % len(1,10)
z2=smooth(x(11:21),x(11:21),0.8,'rloess')'; % len(,10)
z=[z1,z2] % for each part z=[z1,z2... z(end)]

% the code that I am currently using, but I do not understand why such an answer
 step = 10;
 for j = 1:step:size(x,2)-step
    a = y(j:j+1);
    b = x(j:j+1);
    z(1,j+1)= smooth(a,b,0.8,'rloess')';
 end

The answer "z" is not correct (it's a 2,4097 matrix) and there are a lot of zeros in the data.

Thank you in advance

Answer 1

[Mathieu NOE]

hello

not sure what you are trying to do , but if it's about splitting data in buffers and doing some math on the buffers (mean , rms, smooth,..), here maybe some code to help you :

clearvars
% dummy data
n=4097;
x= 1:n;
y = sin(2*pi*x./max(x))+rand(1,n);

buffer = 10;  % nb of samples in one buffer (buffer size) 
overlap = 5; % overlap expressed in samples

%%%% main loop %%%%
m = length(y);
shift = buffer-overlap;    % nb of samples between 2 contiguous buffers  
for ci=1:fix((m-buffer)/shift +1)
    start_index = 1+(ci-1)*shift;
    stop_index = min(start_index+ buffer-1,m);
    time_index(ci) = round((start_index+stop_index)/2);  % time index expressed as sample unit (dt = 1 in this simulation)
    mean_data(ci) = mean(y(start_index:stop_index));  % 

end
x_mean = x(time_index);
figure(1),
plot(x,y,x_mean,mean_data,'r');

[Lev Mihailov]

The code throws this error

Unable to perform assignment because the left and right sides have a different number of elements.

Error in untitled2 (line 12)
    stop_index(ci) = min(start_index+ buffer-1,m);

[Mathieu NOE]

hello Lev

funny, I have no trouble on my release (R2020b)

I just changed now the variable name buffer to mybuffer to avoid potential conflict with matlab's buffer function

clearvars
% dummy data
n=4097;
x= 1:n;
y = sin(2*pi*x./max(x))+rand(1,n);

mybuffer = 10;  % nb of samples in one buffer (buffer size) 
overlap = 5; % overlap expressed in samples

%%%% main loop %%%%
m = length(y);
shift = mybuffer-overlap;    % nb of samples between 2 contiguous buffers  
for ci=1:fix((m-mybuffer)/shift +1)
    start_index = 1+(ci-1)*shift;
    stop_index = min(start_index+ mybuffer-1,m);
    time_index(ci) = round((start_index+stop_index)/2);  % time index expressed as sample unit (dt = 1 in this simulation)
    mean_data(ci) = mean(y(start_index:stop_index));  % 

end
x_mean = x(time_index);
figure(1),
plot(x,y,x_mean,mean_data,'r');
legend('signal','buffered mean');

[Mathieu NOE]

maybe check that you have not used or initialized some of my code's variables from another portion of code that would change arrays dimensions (from my code version)