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I got a strange answer when I use Matlab to calculate the quotient of two decimal places

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I tried to calculate 2.47/0.01,and I got the answer 247.0000. Then I used "ceil" to the answer, and to my surprise, I got the answer 248. This situation doesn't exist when I calculate 24.7/0.1 and 0.247/0.001.

Accepted Answer

Rik on 13 Mar 2023
Welcome to the world of floats and finite precision.
The reason is that some numbers can't be represented exactly by the double data type. The result you showed is displayed with only zeros, but apparently contains something in the decimals that aren't displayed. That is the reason you see .000 in the first place, as Matlab will show integers as integer.
The solution is to test against a tolerance. The eps function may be of use.
  1 Comment
Dyuman Joshi
Dyuman Joshi on 13 Mar 2023
Adding to Rik's point
y = 2.47/0.01
y = 247.0000
num2str(y, 32)
ans = '247.00000000000002842170943040401'
@远东 谢 you can see that the result of operation is not exactly 247 as one would expect.

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