how velocize operation boolean

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pipor
pipor 2023-9-6
评论： Image Analyst 2023-9-6
Ran in:
N = 5
N = 5
a=[0.3 1 0 3 9]
a = 1×5
0.3000 1.0000 0 3.0000 9.0000
b=a<N
b = 1×5 logical array
1 1 1 1 0
find(b&(~a))
ans = 3

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回答（2 个）

Image Analyst
Image Analyst 2023-9-6
That code has nothing to do with your subject line. You want
logicalIndexes = a == 1
% or
linearIndexes = find(a == 1)
Same for b or any other variable.
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pipor
pipor 2023-9-6
Ran in:
a=[0.3 1 0 3 9]
a = 1×5
0.3000 1.0000 0 3.0000 9.0000
n=6
n = 6
b=a<n
b = 1×5 logical array
1 1 1 1 0
a>0
ans = 1×5 logical array
1 1 0 1 1
b
b = 1×5 logical array
1 1 1 1 0
find((a==0)&(~b==0))
ans = 3
Walter Roberson
Walter Roberson 2023-9-6
Ran in:
a=[0.3 1 0 3 9]
a = 1×5
0.3000 1.0000 0 3.0000 9.0000
n=6
n = 6
b=a<n
b = 1×5 logical array
1 1 1 1 0
a>0
ans = 1×5 logical array
1 1 0 1 1
b
b = 1×5 logical array
1 1 1 1 0
find((a==0)&(~(b==0)))
ans = 3
but with b already being logical, b==0 is the same as ~b, and ~ of that is ~~b which for logical would be the same as b

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Image Analyst
Image Analyst 2023-9-6
Ran in:
You asked : "(i want to find idx element that change from 0 to 1 )"
So do this:
a = [5, 0, 1, 9, 0, 1];
index = strfind(a, [0, 1]) % Look for where [0, 1] occurs in the vector.
index = 1×2
2 5
The index is at the start, that is, where the zeros are.
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pipor
pipor 2023-9-6
excuse me a last question:
you use: (b == 1)) but b is logical
why you don't use (b) ..is the same?
Image Analyst
Image Analyst 2023-9-6
(b == 1) will be logical because it's comparing the number to 1. b can be any data type, like double or integer or logical. The result will be true or false values, or 1 and 0 if you convert them to numbers, for example to multiply element-by-element by another numerical vector.
If b is logical than (b) is logical (already). If b is a double vector like [1,2,44,66] then b is not logical -- not true or false values.

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