Error using trapz. Point spacing must be a scalar specifying uniform spacing or a vector of x-coordinates for each data point.

Plot_X = 0:0.01:1;

Per = quantile(SUSC_MO,1:-0.01:0);

for i = 1:101

if i <101

Plot_Y(i) = sum(CAT_M(SUSC_MO>=Per(101-i))) / sum(CAT_M,'all');

else

Plot_Y(i) = sum(CAT_M(SUSC_MO>=0)) / sum(CAT_M,'all');

end

end

AUC= round(100*trapz(Plot_X,Plot_Y),1);

the error is in line 10.

Answer 1

[Voss]

When X and Y are the same length

X = 0:0.01:1;
Y = rand(1,101);

trapz works

trapz(X,Y)

ans = 0.4894

But when X and Y are not the same length

X = 0:0.01:1;
Y = rand(1,102);

the error you saw happens

trapz(X,Y)

Error using trapz
Point spacing must be a scalar specifying uniform spacing or a vector of x-coordinates for each data point.

Therefore, it may be that your Plot_Y is not the same length as your Plot_X. (Perhaps Plot_Y has extra elements from a previous run of your script, for instance, when Plot_X had more than 101 elements.)

If that is the problem, you can correct it by pre-allocating Plot_Y before your for loop:

Plot_X = 0:0.01:1;
% ...
Plot_Y = zeros(size(Plot_X)); % pre-allocate Plot_Y to be a vector of zeros the same size as Plot_X

for i = 1:numel(Plot_X)
    % ...
end