Sum of two numbers is not accepted

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?

Answer 1

[KSSV]

Read about comparing two floating-point numbers.

a=0.14+0.001;
tol = 10^-5 ; 
idx = abs(M(:,2)-a)<=tol ; 
M(idx,:)=[];

Answer 2

[Sriram Tadavarty]

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