How to find the position of a number in an array?

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CS
CS 2020-6-12
编辑： Matt J 2020-6-13
I have a column vector Y which is 7306409x1 double. I want to find the position (indices) of a specifric number (8) in Y. I used
k=find(Y==8)
But MATLAB gives the answer
k =
0×1 empty double column vector
and does not show the indices. I think the problem is something with the "double". Does anyone know how to solve this?
Thanks!

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回答（2 个）

Matt J
Matt J 2020-6-12
编辑：Matt J 2020-6-12
There is nothing wrong with your code as long as there are elements in Y that are exactly equal to 8
>> Y=[8 1 2 5 8 6];
>> k=find(Y==8)
k =
1 5
Suprises may happen, however, if Y contains floating point inaccuracies that you can't see on the screen,
>> Y=[8 1 2 5 8 6] + 10*eps,
Y =
8.0000 1.0000 2.0000 5.0000 8.0000 6.0000
>> k=find(Y==8)
k =
1×0 empty double row vector
One solution is to round,
>> k=find(round(Y)==8)
k =
1 5
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CS
CS 2020-6-12
format long will show the long format of numbers in the command window. My question is regarding to how show the long format of numbers in the Variables window?
Matt J
Matt J 2020-6-13
编辑：Matt J 2020-6-13
My question is regarding to how show the long format of numbers in the Variables window?
That can be adjusted in the view tab
However, rather than relying on copy-paste, I think it would be better to simply do,
k=find(Y==Y(283))

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madhan ravi
madhan ravi 2020-6-12
编辑：madhan ravi 2020-6-12
k = find( (abs(Y) - 8) < 1e-2 ) % where 1e-2 is the tolerance

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