About logical calculation. Is this a bug?

Question

Jingli Xie 2020-1-14

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/500181-about-logical-calculation-is-this-a-bug

评论： Steven Lord 2020-1-14

采纳的回答： Adam Danz

what happened to this case? Is this a matlab bug?

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Jingli Xie 2020-1-14

logical should be 1 at the lower left corner of the picture.

-1<p_grad == 1, p_grad < 1 ==1, bug -1<p_grad<1 == 0

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Adam Danz 2020-1-14

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/500181-about-logical-calculation-is-this-a-bug#answer_410001

编辑：Adam Danz 2020-1-14

在 MATLAB Online 中打开

The operation

p_grad = 1.1200e-17; 
-1 < p_grad < 1

works from left-to-right. It is interpretted as

p_grad = 1.1200e-17; 
(-1 < p_grad)  <  1

which is simplified to

1 < 1

which equals 0 (false).

To determine if p_grad is between -1 and 1, (parentheses optional)

(-1 < p_grad)  &&  (p_grad < 1)      % for scalar values
(-1 < p_grad)  &  (p_grad < 1)       % for non-scalar values or when
                                     % number of element is unknown

3 个评论
显示 1更早的评论隐藏 1更早的评论

Stephen23 2020-1-14

Also note that the A<B<C syntax does not exist in the MATLAB documentation:

https://www.mathworks.com/help/matlab/logical-operations.html

https://www.mathworks.com/help/matlab/matlab_prog/operator-precedence.html

Steven Lord 2020-1-14

If I remember correctly, as of release R2019b if you try to use that idiom in a file in the Editor Code Analyzer will warn you that it doesn't do what you think it does.

请先登录，再进行评论。