Sum(X) = 1 but Sum(X)==1 produces logical 0

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George
George 2014-7-22
评论： George 2014-7-22
Can someone please explain this?
sum([Node(temp).pbelief])
ans =
1.0000
K>> sum([Node(temp).pbelief])==1
ans =
0
By the way:
Node(temp(1)).pbelief
ans =
0.0024
K>> Node(temp(2)).pbelief
ans =
0.9976

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采纳的回答

Namita Vishnubhotla
This does not seem like a limitation/bug in MATLAB. Use the long fixed decimal format before displaying your values:
>> format long
There is a possibility for a discrepancy in the values.
For example, sum([Node(temp).pbelief]) could actually hold 1.0000100, in which case the equality condition is bound to fail.
You could also use "format hex" to view the hexadecimal representation of your sum, and compare it to the hexadecimal representation of 1.
In general, it is not advisable to compare the equality of two values directly, as you have done in this case. It is better to compare their difference to a small predefined tolerance value.
>> abs(sum([Node(temp).pbelief]) – 1) <= 0.0001

更多回答（2 个）

Sean de Wolski
Sean de Wolski 2014-7-22
James Tursa
James Tursa 2014-7-22
Note that when a number is exactly an integer, and you are only printing one scalar value, MATLAB prints it without any trailing 0's. But if the number is not exactly an integer, MATLAB will print trailing 0's, indicating that there is a non-zero digit down the line somewhere even if it is not printed to the screen. E.g.,
>> format short
>> 1
ans =
1
>> 1.0000001
ans =
1.0000

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