How Can I Clearly Identify Differences? and How to Save and Display Data in Full Decimal Format?

Hi, I have 2 data and I would like to check the differences.

According to Matlab, when I minus both data, it shows differences but when I copy the data directly from the Matlab workspace and minus it in MS Excel. it appears 0 (no differences) as shown in the attachment.

May I know how to see its difference in Matlab because I can't see any differences? And how to save and see all the data in full decimal? Is there a way to make the data tally in Excel and Matlab?

Below are the codes.

clear
clc

format long

load QuestionWorkspace

Data1

Data1 = 
   0.998003837794450

Data2

Data2 = 
   0.998003837794450

% It seems like no different but why there is different value after deduct it ?
Difference_Value= Data1-Data2

Difference_Value = 
     2.220446049250313e-16

% How to see its different?
% However, when I copy the data in excel
% minus the both data it appears 0 ... no different...

% How to save and see all the data in full decimal? 

Thanks in advance.

Answer 1

[DGM]

I'm going to assume that you're entering them into excel by trusting that

format long

will reveal the entire number. It won't really. You can get more digits other ways, though be aware that when changing base, you're not assured that the result actually can be represented in a finite number of digits. At some point, the results you get will just be junk.

load QuestionWorkspace

fprintf('%.18f\n',Data1)

0.998003837794449788

fprintf('%.18f\n',Data2)

0.998003837794449566

We can see that the numbers are definitely not the same, but if you had copied them from the console window using the formatting you'd used before, then you're reducing the precision enough that they are the same.

Alternatively, please consider that I haven't used Excel in a decade, and I don't use the modern tools for writing to xlsx files. If for some reason, the data were converted to single precision floats, then you'd lose enough precision that the numbers would indeed become equal.

[Wei Wen]

Thank you for the explaination.