A bug? input: 1/0 output: -Inf

Question

qilin 2024-2-13

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2081468-a-bug-input-1-0-output-inf

评论： Matt J 2024-2-13

采纳的回答： Stephen23

x.mat

在 MATLAB Online 中打开

if x=0, expected output of 1/x is Inf, but matlab output -Inf

load('x.mat')
x==0
Unrecognized function or variable 'x'.
1/0
1/x

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Matt J 2024-2-13

Your attached file doesn't contain a variable called x.

Image Analyst 2024-2-13

x==0 is a comparison, not an assignment. Since you didn't assign x yet, you can't see if it's equal to zero, hence the error. I think you meant x=0, not x==0.

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Answer 1

Stephen23 2024-2-13

3
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2081468-a-bug-input-1-0-output-inf#answer_1407608

编辑：Stephen23 2024-2-13

在 MATLAB Online 中打开

"A bug? input: 1/0 output: -Inf"

Not a bug. Because your value x is actually negative zero not positive zero:

https://en.wikipedia.org/wiki/Signed_zero

Lets try it now:

x = -0
x = 0
1/x
ans = -Inf
num2hex(x) % yep, definitely negative zero
ans = '8000000000000000'
x = +0
x = 0
1/x
ans = Inf
num2hex(x) % yep, that is positive zero
ans = '0000000000000000'

So far everything is working exactly as expected. Note that a few simple arithmetic operations will convert negative zero to positive zero without affecting any other values, e.g. adding zero:

x = -0;
1/x
ans = -Inf
x = 0+x;
1/x
ans = Inf

4 个评论
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Dyuman Joshi 2024-2-13

How did you obtain that value?

Stephen23 2024-2-13

"maybe the next step is to figure out why my ''deltaX'' is negative zero"

Most likely it makes zero(!) difference: note that by definition negative and positive zeros have the same value, so if you are happy with your array being zero-value then simply multiply your array by one (or add zero) and move on to more important tasks.

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