Error using corrcoef. x and y must have the same number of elements....?

Hi everyone!

Running some fMRI stuff and we are having some trouble trying to figure out what Error using corrcoef X and Y must be have the same number of elements

for r=1:roiN

fcmap=zeros(1,numpix); %1-by-#num voxels in 3D volume

seedts=load([roiList{r},'_','residvol_ts.txt']);

for pix=1:size(fcmap,2) %1 to #num voxels in 3D volume

tmp=corrcoef(seedts,func(:,pix)); %calc correlation bewteen seed timeseries and timeseries of that voxel; tmp=2x2 symmetric corr table

pixr=tmp(1,2);

fcmap(pix)=pixr; %fill voxel with correlation coefficient

if doFisherZ

fcmap(pix)=(.5*log((1+pixr)/(1-pixr)));

else

end

end

Thanks for your help :)

[Mathieu NOE]

yeap

read the doc

% this work
A = randn(10,1);
B = randn(10,1);
R = corrcoef(A,B)

R = 2×2

1.0000 0.3131 0.3131 1.0000

% this doesn't work
A = randn(10,1);
B = randn(12,1);
R = corrcoef(A,B)

Error using corrcoef
X and Y must have the same number of elements.

Answer 1

[Dinesh]

Hi Ryu!

Here in this line of code

tmp=corrcoef(seedts,func(:,pix)); 

The time series seed array and time series voxel are not having same number of elements and without same number of elements we cannot calculate correlation coefficent. Despite how they are shaped to calculate corrcoeff we need to have same number of elements.

For more Details on how correlation coefficient is calculated and it's internal mathematics please refer the following MATLAB Documentation