X is rank deficient to within machine precision. Linear regression of mean

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aine gormley
aine gormley 2018-11-17
编辑： aine gormley 2018-11-17
Hello, so I am writing code to do a linear regression on 2 variables - each variable exists on 5 different nc files, so I have to draw the data from them first.
The code is below. It is generating sensible figures and statistics. However, I keep getting the amber warning:
"Warning: X is rank deficient to within machine precision"
>In regress (line 84)
>In mean_ctl2 (line 54)
Is this perhaps because the code is generating the mean slopes (rather than the slope of the mean variable)?
% Loop through the five files - 001 to 005, read and save what is needed
num_files = 5;
for i = 1 : num_files
lat = ncread(sprintf('f.io192.00%d_atm_h1_yearmean_selname.nc', i), 'lat');
lon = ncread(sprintf('f.io192.00%d_atm_h1_yearmean_selname.nc', i), 'lon');
time = ncread(sprintf('f.io192.00%d_atm_h1_yearmean_selname.nc', i), 'time');
TSA = ncread(sprintf('f.io192.00%d_lnd_h1_yearmean_selname.nc', i), 'TSA');
TXx = ncread(sprintf('f.io192.00%d_atm_h1_yearmean_selname.nc', i), 'TXx');
TXxs = cat(4, TXxs, TXx);
TSAs = cat(4, TSAs, TSA);
end
% Create storage for regression
% Number of lat and lon and times must be the same across all 5 files
M = numel(lon);
N = numel(lat);
slope_TXx = zeros(M, N, num_files);
intercept_TXx = zeros(M, N, num_files);
slope_TSA = zeros(M, N, num_files);
intercept_TSA = zeros(M, N, num_files);
T = numel(time);
% Regress each lat/lon location
for i = 1 : M
for j = 1 : N
% Take each file
for k = 1 : num_files
% Get all time instances of each lat/lon location for TXx
y = squeeze(TXxs(i, j, :, k));
% Create regression problem and solve
x = [ones(T, 1) time];
%c = x \ y;
c = regress(y, x);
intercept_TXx(i, j, k) = c(1);
slope_TXx(i, j, k) = c(2);
% Repeat for TSA
y = squeeze(TSAs(i, j, :, k));
% Create regression problem and solve
%x = [ones(T, 1) time];
%c = x \ y;
c = regress(y, x);
intercept_TSA(i, j, k) = c(1);
slope_TSA(i, j, k) = c(2);
end
end
end
% Find the mean of each file
mean_slope_TXx = mean(slope_TXx, 3);
mean_slope_TSA = mean(slope_TSA, 3);
mean_intercept_TXx = mean(intercept_TXx, 3);
mean_intercept_TSA = mean(intercept_TSA, 3);

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