Dot indexing is not supported for variables of this type in a for loop

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Hello everyone,
I am trying to execute this code and I am having the following error:
clc;clear;close all
addpath('/media/hf9098/easystore/MATLAB/POD')
SnapshotsAddress = pwd; % put current path here
files = dir(fullfile(SnapshotsAddress,'data_*.txt'));
n_snapshots = natsortfiles(files);
if iscell(n_snapshots) == 0;
n_snapshots = (n_snapshots);
end
n_snapshots = size(files,1);
for j = 1:numel(n_snapshots)
folder = n_snapshots(j).folder;
filename = n_snapshots(j).name;
fid = fullfile(n_snapshots(j).folder,n_snapshots(j).name);
data = dlmread(fid);
x = data(1,:) % x coordinate
y = data(2,:) % y coordinate
U(j,:) = data(4,:); % u velocity
V(j,:) = data(5,:); % v velocity
end
%Section 2 -­‐ Compute spatial correlation matrix C
c1 = U*U';
c2 = V*V';
C = (c1+c2)/n_snapshots;
%Section 3 -­‐ Solve the eigenvalue problem: C * EigenVector = EigenValue * EigenVector
[beta, lmd] = svd(C);
%Section 4 -­‐ Calculate basis functions
phix = U'*beta;
phiy = V'*beta;
% Normalize basis functions
GridNum = size(x,2);
for j=1:n_snapshots
PhiNor = 0;
for i=1:GridNum
PhiNor = PhiNor + phix(i,j)^2 + phiy(i,j)^2;
end
PhiNor = sqrt(PhiNor);
phix(:,j)= phix(:,j)/PhiNor;
phiy(:,j)= phiy(:,j)/PhiNor;
end
%Section 5 -­‐ Calculate coefficient
TimCoeU = U*phix;
TimCoeV = V*phiy;
TimCoe = TimCoeU + TimCoeV;
%Section 6 -­‐ Export basis functions
for a=1:n_snapshots
FilNamPhi = 1000+a;
PhiOut = fopen([SnapshotsAddress,num2str(FilNamPhi),'.txt']', 'wt');
fprintf(PhiOut, '#DaVis 7.2.2 2D-­‐vector 16 145 145 "position" "mm" "position" "mm" "velocity" "m/s"\n');
phia = [x;y;phix(:,a)';phiy(:,a)'];
fprintf(PhiOut, '%20.9f %20.9f %20.9f %20.9f\n',phia);
fclose(PhiOut);
end
% Write coefficients into excel file
xlswrite([SnapshotsAddress,'TimCoe.xlsx'],TimCoe);
The error is:
Dot indexing is not supported for variables of this type.
Error in VelocityDistributionPOD (line 57)
folder = n_snapshots(j).folder;
Even upon commenting line57, it is still present in line58 and line59
Any thoughts how to override such error?
Thank you!

Accepted Answer

Steven Lord
Steven Lord on 12 Jan 2023
First:
n_snapshots = natsortfiles(files);
n_snapshots was a struct array. But then:
if iscell(n_snapshots) == 0;
n_snapshots = (n_snapshots);
end
n_snapshots = size(files,1);
you changed it to a scalar double. Change one of the variable names to something more indicative of its purpose.

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