MOD bug? Or something else?

3 次查看（过去 30 天）
Dr. Seis
Dr. Seis 2012-10-4
Seems to be a bug in MOD. The values inside the range from 0 to 1 that should result in MOD of 0 (or 0 to machine precision) for the example below (i.e., 0.4 and 0.8) are no where near 0.
>> [-2:.2:2;mod(-2:.2:2,.4)]'
ans =
-2.0000 0
-1.8000 0.2000
-1.6000 0
-1.4000 0.2000
-1.2000 0
-1.0000 0.2000
-0.8000 0.0000
-0.6000 0.2000
-0.4000 0.0000
-0.2000 0.2000
0 0
0.2000 0.2000
0.4000 0.4000
0.6000 0.2000
0.8000 0.4000
1.0000 0.2000
1.2000 0
1.4000 0.2000
1.6000 0
1.8000 0.2000
2.0000 0
I am running R2011a on UNIX... anyone else encounter this problem?

请先登录，再回答此问题。

采纳的回答

Matt Fig
Matt Fig 2012-10-4
编辑：Matt Fig 2012-10-4
Floating point arithmetic.... Look closely at the numbers.
x = [-2:.2:2];
fprintf('%16.16f\n',x)
You can read more about it here.
  1 个评论
Dr. Seis
Dr. Seis 2012-10-4
Yep... I was thinking this had nothing to do with floating point stuff. But if the value was very close to 0.4 (i.e., 0.4 +/- epsilon), the behavior of MOD would be very different if it was +epsilon versus -epsilon.
mod(0.39999999999,0.4) = 0.39999999999
vs.
mod(0.40000000001,0.4) = 0.00000000001
Looks like I will need to overload MOD

请先登录，再进行评论。

更多回答（1 个）

Dr. Seis
Dr. Seis 2012-10-5
This overloaded MOD function seems to overcome my issue:
function answer = mod(X,Y)
tol = 1e7;
X = round(X*tol)/tol;
Y = round(Y*tol)/tol;
answer = builtin('mod',X,Y);
end
*Note: I am dealing with numbers with less than 7 significant digits

类别

在 Help Center 和 File Exchange 中查找有关 Introduction to Installation and Licensing 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by