Facing this weird comparison error of vector

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评论： Mahesh Babu Dhanekula 2020-10-27

I have some data that needs to be read from a file.

contents of file are as follows:

point1

0,0,2.2

point2

1,0,2.2

so i have used the fread command to read contents and used the Newline command to store each line as a member of cell(4x1 in this case).

I used the following command to convert the point data in form of string into vector

A = str2num(strtrim(Lines{2}))
D = str2num(strtrim(Lines{4}))
Outputs: (Double)
A = [0,0,2.2000]
D = [1,0,2.2000]

Here comes the error when i tried to compare the 3rd elements of A & D and to my surprise the following comparison expression false:

A(3) == D(3)

ans = 0 (logical)

Can anybody say what is wrong in this that causing this type of result ?

Please share your thoughts

Stephen23 2020-10-27

编辑：Stephen23 2020-10-27

"I forgot to add a point about i am modifying one point to get the vertices of geometry"

Ah, secret operations that accumulate floating point error :)

"Here after i am facing this comparison error as you said it might be attributed to floating point error."

Yes.

Use this to look at the exact values, you will see that they are not the same:

Tip: do not test floating point numbers for exact equivalence. Always compare the absolute difference against a tolerance:

abs(X-Y)<tol

Thanks Stephen, I will modify my logic accordingly.

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