Code only works sometimes when run
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this code works some of the time i run it, but not others.
i.e. i and j will display some of the time when the script is run, but most often they will not
A = randi(5, 4, 4, 3);
size = numel(A);
n = randperm(size, 1);
[i j] = find(A==n);
disp([i,j])
any ideas why? cheers
4 个评论
Ideas? Sure. :)
Hint: What does numel(A) return?
PS. Don't use size as a variable; that aliases the builtin size() function and that will cause consternation elsewhere...
PPS. It works every time; it just illustrates that just having code that doesn't have any syntax error doesn't mean the logic is correct to solve the problem! :) While it is a necessary condition, it isn't sufficient.
We don't know what the actual intent was so we don't know what the actual solution would be.
Image Analyst
2018-9-3
It's also a good idea not to use i and j because they are the built in imaginary variables.
采纳的回答
"any ideas why?"
Because you test for numbers that do not exist in A, and so the output is empty.
Lets have a look at an example:
>> A = randi(5, 4, 4, 3) % 4x4x3 array of values 1-5.
A(:,:,1) =
1 3 1 3
4 3 1 1
1 1 5 4
5 3 5 3
A(:,:,2) =
1 2 1 1
5 3 1 5
1 5 2 5
1 1 2 4
A(:,:,3) =
4 2 3 1
5 2 2 1
2 4 2 3
5 2 5 4
>> S = numel(A) % do NOT use SIZE as a variable name!
S = 48
>> n = randperm(S,1) % could be 1-48.
n = 7
But are any of the values in A equal to 7? Of course not, because you specified that the values of A must be 1-5. So for most random values of n (from 6-48), there will be absolutely no matches:
>> A==n
ans(:,:,1) =
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
ans(:,:,2) =
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
ans(:,:,3) =
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
>> find(A==n)
ans = []
What do you expect to happen when you test for values that do not exist?
更多回答（1 个）
Hi,
in addition to the valueable comments:
What you do is make a Matrix A with the dimensions: 4 x 4 x 3 which means it has 48 elements. These elements are randomly between 1...5
Then you create 1(!) random number n between 1...48
Then you want to get the indicies of all occurences from this one number in A.
The chance that n is in the Matrix = 5/48 ~ 10,42% --> Thats because you will only get indices back from the find function if n = [1...5]
At about 90% of all cases you test this, you will get nothin back, because n = [6...48]
I guess this is not the bahavior you wanted, but it is what you have written in your code.
Best regards
Stephan
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