I have this code which is behaving differently for decimal and integer values. Where am I missing??
显示 更早的评论
x=0.1;
y=0.1;
a=[x,y];
b=[0.2,0.2];
tf=isequal(a,b);
while tf==0
x=x+(0.01);
y=y+(0.01);
a=[x,y];
tf=isequal(a,b);
end
disp(a);
if i replace the x, y and incremental values by integers, it works !! for ex as shown below
x=1000;
y=1000;
a=[x,y];
b=[2000,2000];
tf=isequal(a,b);
while tf==0
x=x+1;
y=y+1;
a=[x,y];
tf=isequal(a,b);
end
disp(a);
5 个评论
EDIT: See Stephen's answer below.
A possible workaround is to convert the floating point numbers to characters to compare them:
tf=(isequal(sprintf('%c',a),sprintf('%c',b)));
dpb
2018-5-31
Paolo
2018-5-31
Thanks for the clarification Stephen, I forgot to take into consideration the accumulating error.
akash sonnad
2018-5-31
采纳的回答
Stephen23
2018-5-31
"That is really weird indeed. Perhaps MATLAB struggles to determine equality for floating point numbers"
Not at all: if two numbers are really equal, then MATLAB will correctly identify them as such. The only struggle here is beginners who believe that 0.1 is really stored in their computer, and have yet to learn that floating point number errors accumulate through all computations. Which means that those numbers are NOT equal.
"Where am I missing??"
Never use == to test for equivalence of decimal values. Always compare the difference against a tolerance:
abs(A-B)<tol
And some external links on this topic:
The solution is always the same, as shown in all of those links: compare the absolute difference against a tolerance, like this:
abs(A-B)<tol
Methods to be avoided: converting to string is very slow, and rounding the values introduces artifacts that do not exist in the data.
更多回答（0 个）
类别
在 帮助中心 和 File Exchange 中查找有关 Entering Commands 的更多信息
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!
Translated by 
