Sum of two numbers is not accepted

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Stanislav Kotsmid
Stanislav Kotsmid 2020-7-30
回答： Sriram Tadavarty 2020-7-30
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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KSSV
KSSV 2020-7-30
编辑：KSSV 2020-7-30
Read about comparing two floating-point numbers.
a=0.14+0.001;
tol = 10^-5 ;
idx = abs(M(:,2)-a)<=tol ;
M(idx,:)=[];

更多回答（1 个）

Sriram Tadavarty
Sriram Tadavarty 2020-7-30
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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