Weird-Confusing mistake in subtraction result!!!!

2 次查看（过去 30 天）
shirin mhd
shirin mhd 2022-8-25
移动：Matt J 2022-8-25
Hi everyone
I have a weird problem with a simple subtraction.
Here is my code. I define 'R' and 'a1 to a8':
R=194067676.886295
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
a1=19044444.410581;
a2=15000000.000000;
a3=1500000.000000;
a4=4000000;
a5=500000;
a6=32323232.475714;
a7=120000000;
a8=1700000;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
sum=a1+a2+a3+a4+a5+a6+a7+a8
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
d=sum-R
As you can see from the result below, the value of 'R' and 'sum' is the same.
I expect the subtraction of 'R' and 'sum' which is 'd', becomes zero.
But as you can see, it isn't zero and I don't understand why is this happening.
result:
R =
1.940676768862950e+08
sum =
1.940676768862950e+08
d =
2.980232238769531e-08
please help me with this problem.
I'm really confused.

请先登录，再回答此问题。

采纳的回答

Stephen23
Stephen23 2022-8-25
移动：Matt J 2022-8-25
"Weird-Confusing mistake"
Not weird, not a mistake, but perhaps confusing to the uninitiated.
"please help me with this problem."
Read about binary floating point numbers:
https://www.mathworks.com/matlabcentral/answers/57444-faq-why-is-0-3-0-2-0-1-not-equal-to-zero
https://www.mathworks.com/matlabcentral/answers/316889-why-two-equal-numbers-are-not-equal
http://www.mathworks.com/matlabcentral/answers/102419-how-do-i-determine-if-the-error-in-my-answer-is-the-result-of-round-off-error-or-a-bug
http://www.mathworks.com/matlabcentral/answers/140656-about-numerical-difficulty-of-equality-comparison-operation-between-two-double-real-numbers-in-matlab
This is worth reading as well:
https://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html
http://faculty.tarleton.edu/agapie/documents/cs_343_arch/papers/1991_Goldberg_FloatingPoint.pdf
  1 个评论
shirin mhd
shirin mhd 2022-8-25
移动：Matt J 2022-8-25
I really appreciate your taking the time to explain the concept and share links. Im a novice coder and I'm learning a lot from here. Thank you for your help.

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 Logical 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