Why fprintf('%3.1f',round(-eps)) prints -0.0?
조회 수: 5 (최근 30일)
이전 댓글 표시
I found some very strange behaviour of the round function in Matlab R2016b (at least for me). I would expect that the round function returns 0 for -eps, but surprisingly the command:
num2hex(round(-eps))
Returns:
8000000000000000
Instead of
num2hex(0) == 0000000000000000
This causes fprintf() to print -0.0. Is this a bug or I just miss something?
댓글 수: 1
James Tursa
2017년 1월 17일
Side Note: This seems to be consistent among the related functions ceil and fix as well. E.g.,
>> num2hex(round(-eps))
ans =
8000000000000000
>> num2hex(ceil(-eps))
ans =
8000000000000000
>> num2hex(fix(-eps))
ans =
8000000000000000
채택된 답변
Stephen23
2017년 1월 17일
편집: Stephen23
2017년 1월 17일
You are missing the fact that MATLAB has two zeros: positive zero and negative zero, which have different HEX values. This is a result of the IEEE 754 floating point standard that MATLAB implements, which uses one bit to indicate the number sign: a corollary of this is that even a zero can be positive or negative.
It is not possible to use < to directly test if zero is negative (by definition negative zero is equal to positive zero, so this makes sense):
>> (-0)<0
ans =
0
but here is one simple trick that will test for negative zero:
>> (1/-0)<0
ans =
1
Which relies on this behavior:
>> 1/-0
ans =
-Inf
>> 1/round(-eps) % your question
ans =
-Inf
Neat huh!
You can find more interesting information on negative zeros here:
댓글 수: 0
추가 답변 (1개)
참고 항목
카테고리
Help Center 및 File Exchange에서 Logical에 대해 자세히 알아보기
제품
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!