How to fix the precession difference error of variables in matlab?

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I have 2 data sets named T and T2 as shown in the below figure with values ranging with a precession of 1e-5.
The expected max difference of T1-T2 should appear at Sample number 20 through visual inspection from figure 1. However, when I plot T1-T2 in matlab, I get completely a wrong plot as shown below with sample number 44 as maximum of difference, which is not true. In this regard, could some one help me to solve this issue.

Accepted Answer

Dyuman Joshi
Dyuman Joshi on 23 Aug 2022
Edited: Dyuman Joshi on 23 Aug 2022
If you look at the values, you will get an idea as to why that's happening -
format long
T1=load('T1.mat').T1;
T2=load('T2.mat').T2;
T1(20)
ans =
5.116663670052163e-07
T2(20)
ans =
1.247071549704016e-10
T1(20)-T2(20)
ans =
5.115416598502459e-07
T1(44)
ans =
6.325269098750142e-06
T2(44)
ans =
5.813727438899893e-06
T1(44)-T2(44)
ans =
5.115416598502488e-07
As the values increase, on graph it may look like the difference is smaller but that is compared to the original values (absolute scale). If you want to get a clear idea, compare on an relative scale.
%comparing to T1
plot(1:numel(T1),(T1-T2)./T1)
%comparing to T2
plot(1:numel(T1),(T1-T2)./T2)
Now you can see the spike is near 20, as you observed

More Answers (1)

Abderrahim. B
Abderrahim. B on 23 Aug 2022
You are replying on what your eyes see, use max function.
clear
close all
load(websave("T1", "https://www.mathworks.com/matlabcentral/answers/uploaded_files/1105360/T1.mat"))
load(websave("T2", "https://www.mathworks.com/matlabcentral/answers/uploaded_files/1105365/T2.mat"))
figure
subplot(2,1,1)
plot(T1)
hold on
plot(T2)
subplot(2,1,2)
plot(T1 - T2)
[maxV idx] = max(T1 -T2) % the plot is correct
maxV = 5.1154e-07
idx = 44

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