I am trying to perform the vector sum below. Why am I getting 0.0000 in the 3rd entry when I should be getting 0

2 次查看（过去 30 天）
Eddie
Eddie 2017-1-21
评论： Walter Roberson 2017-1-29
[-1/14 -1/7 -3/14 0] - 1/5*[9/14 9/7 -15/14 0]
= -0.2000 -0.4000 0.0000 0
Thank you.

请先登录，再回答此问题。

采纳的回答

Walter Roberson
Walter Roberson 2017-1-21
http://matlab.wikia.com/wiki/FAQ#Why_is_0.3_-_0.2_-_0.1_.28or_similar.29_not_equal_to_zero.3F
The fractions 1/5, 1/7 and 1/14 are not exactly representable in finite binary floating point, just the same way that 1/7 and 1/14 cannot be exactly represented in finite decimal expansion.
It is much the same problem as representing 1/3 as 0.33 . Add that together three times and you get 0.99 instead of 1, as the truncation losses build up.
  6 个评论
显示 4更早的评论
Eddie
Eddie 2017-1-28
Wow thank you so much for the input. Nope I did not initialize i and j, and only because I didn't see a need to, and now I do. I'll make the changes you recommended, take care.
Walter Roberson
Walter Roberson 2017-1-29
Your "for" loops are initializing i and j okay; I was discussing in general how it can be hard in code to notice that you did not initialize variables. Failure to initialize becomes more obvious if you are using a variable name that is not i or j or pi (or inf or NaN or nan !), but if you happen to use one of those as a variable name then you can end up staring at the code for a long time trying to figure out what is going wrong. So good coding practice is to avoid using any of those as variable names.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Code Performance 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