Why is logical array fasle?

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Hitesh Pradhan
Hitesh Pradhan 2021-6-15
回答： Kunal Kandhari 2021-6-15
SCRIPT WINDOW
g=9.8000 %value for g
p=3.14; %value of mathematical pie
k1=3.1210191*p
k1==g %generation of logical array
COMMAND WINDOW
g =
9.8000
k1 =
9.8000
ans =
logical
0

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回答（3 个）

Scott MacKenzie
Scott MacKenzie 2021-6-15
The result is false because k1 DOES NOT EQUAL g
Note that both k1 and g are scalars, not vectors. Therefore, the result of k1==g is a logical scalar which is false or 0.
Steven Lord
Steven Lord 2021-6-15
Floating point arithmetic. While k1 and g are displayed the same they do not contain the same value down to the last bit.
Kunal Kandhari
Kunal Kandhari 2021-6-15
It is because most decimal fractions are not exactly representable in binary form, just like 1/3 is not representable exactly in a finite number of decimal digits.
if you print 55 decimal places of both the variables you will get something like this:
sprintf('%0.55f',k1)
'9.7999999740000003356499291840009391307830810546875000000'
sprintf('%0.55f',g)
'9.8000000000000007105427357601001858711242675781250000000'
NEVER compare two floating point doubles for exact equality. Well, there are some notable exceptions. So unless you know the exceptions, then assume never applies.
You can see a very detailed description of the same here:
https://matlab.fandom.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F

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