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Sum of two numbers is not accepted

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Hi everyone,
I have a problem with deleting numbers in a matrix. Let's have a matrix M, where I want to delete all rows with a specified value in the second column, e.g:
M(M(:,2)==0.141,:)=[];
All rows with 0.141 in the second column are now deleted.
Also, I tried to specify this value by a sum of two numbers:
a=0.14+0.001;
M(M(:,2)==a,:)=[];
This sum hasn't been accepted and all values are still in the matrix.
Can anyone explain me this mysterious thing please?

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Accepted Answer

KSSV
KSSV on 30 Jul 2020
Edited: KSSV on 30 Jul 2020
Read about comparing two floating-point numbers.
a=0.14+0.001;
tol = 10^-5 ;
idx = abs(M(:,2)-a)<=tol ;
M(idx,:)=[];

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More Answers (1)

Sriram Tadavarty
Sriram Tadavarty on 30 Jul 2020
Hi Stanislav,
It is the way the floating point airthmetic are performed in MATLAB.
If you would have tried 0.14 + 0.001 equals 0.141, then you would have seen both doesn't match.
There were similar posts in this forum regarding this. One such which i recently encountered has lot more detailed links. https://www.mathworks.com/matlabcentral/answers/572680-is-there-a-bug-in-the-if-function
Also, inorder to avoid common problems using airthmetic floating point numbers, have a look here.
For the problem here, place a tolerance and then it would provide same results, as expected.
Thanking you.
Regards,
Sriram

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