Matlab adds a minor number to integer - why?

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Oded T
Oded T 2019-5-5
回答： Stephen23 2019-5-5
hi,
i noticed a very strange phenomanon:
i defined a few numbers:
t1 = 18.1
Delta = 0.1
t2 = t1 + Delta;
now open the cell of t2 and i see matlab add some very small value in the end of the decimal number, i.e.:
t2 = 18.200000000000003
what is the "3" in the end and how can i prevent it from happening?
I need the exact numbers and not additions,
tnanks,
Oded

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回答（1 个）

Stephen23
Stephen23 2019-5-5
"i noticed a very strange phenomanon:"
Nope, not strange at all.
"what is the "3" in the end..."
Accumulated floating point error.
"...and how can i prevent it from happening?"
You can't. All operations on floating point values have the potential to collect floating point error. It is simply fundemental to how those values are stored. You need to learn about the limits of floating point numbers. Start by reading these:
https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero
https://www.mathworks.com/matlabcentral/answers/316889-why-two-equal-numbers-are-not-equal
http://www.mathworks.com/matlabcentral/answers/102419-how-do-i-determine-if-the-error-in-my-answer-is-the-result-of-round-off-error-or-a-bug
http://www.mathworks.com/matlabcentral/answers/140656-about-numerical-difficulty-of-equality-comparison-operation-between-two-double-real-numbers-in-matlab
This is worth reading as well:
https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html
http://faculty.tarleton.edu/agapie/documents/cs_343_arch/papers/1991_Goldberg_FloatingPoint.pdf

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