Problem with if function and decimal numers

2014 1 13
2 个回答
回答已采纳
更新时间：2014 1 13
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0 个投票

Good evening, i have a problem with this code:
a=1:0.1:2;
b=0.1;
for i=1:1:10
angoloutile(i)=a(i);
end
for j=1:1:10
integ = fix(angoloutile(j)) ;
fract = abs(angoloutile(j)- integ);
if fract == b
angoloutile(j)=angoloutile(j)+0.5
end
end
for k=1:1:10
angoloutile(k)
end
it doesn't take the IF function
if fract == b
but i'm sure that angoloutile(2) is 1.1 Thanks

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 采纳的回答

Image Analyst
Image Analyst 2014-1-13

1 个投票

The problem was using fix instead of rounding. Try this where I use int32() to cast to the nearest integer. I also cleaned up your if to make it more efficient and reduce the number of if tests by a factor of 10.
a=1:0.1:2;
for i=1:1:10
angoloutile(i)=a(i);
end
for j=1:1:10
integ = fix(angoloutile(j));
fract = abs(angoloutile(j)- integ);
fract=fract*10;
deci=int32(fract);
fprintf('j = %d, angoloutile(j) = %f, integ = %d, fact = %f, deci = %d\n', ...
j, angoloutile(j), integ, fract, deci);
if deci == 1
angoloutile(j)=angoloutile(j)+0.5;
elseif deci == 2
angoloutile(j)=angoloutile(j)-0.08;
elseif deci == 3
angoloutile(j)=angoloutile(j)-0.12;
elseif deci == 4
angoloutile(j)=angoloutile(j)-0.16;
elseif deci == 5
angoloutile(j)=angoloutile(j)-0.20;
elseif deci == 6
angoloutile(j)=angoloutile(j)-0.24;
elseif deci == 7
angoloutile(j)=angoloutile(j)-0.28;
elseif deci == 8
angoloutile(j)=angoloutile(j)-0.32;
elseif deci == 9
angoloutile(j)=angoloutile(j)-0.36;
end
end
% Print to command window.
angoloutile

更多回答（1 个）

Amit
Amit 2014-1-13

0 个投票

The issue is very small difference in floating point numbers, like 1.00000 and 1.0000000001. There is negligible difference however they are not equal. You can do something like:
tol = 1e-6;
if (fract-b) < tol
This will work.

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Nicola
Nicola 2014-1-13
I'm sorry but your answer doesn't work for me. I changed the code and now is:
a=1:0.1:2;
for i=1:1:10
angoloutile(i)=a(i);
end
for j=1:1:10
integ = fix(angoloutile(j));
fract = abs(angoloutile(j)- integ);
fract=fract*10;
deci=fix(fract);
if deci == 1
angoloutile(j)=angoloutile(j)+0.5;
end
if deci == 2
angoloutile(j)=angoloutile(j)-0.08;
end
if deci == 3
angoloutile(j)=angoloutile(j)-0.12;
end
if deci == 4
angoloutile(j)=angoloutile(j)-0.16;
end
if deci == 5
angoloutile(j)=angoloutile(j)-0.20;
end
if deci == 6
angoloutile(j)=angoloutile(j)-0.24;
end
if deci == 7
angoloutile(j)=angoloutile(j)-0.28;
end
if deci == 8
angoloutile(j)=angoloutile(j)-0.32;
end
if deci == 9
angoloutile(j)=angoloutile(j)-0.36;
end
end
for k=1:1:10
angoloutile(k)
end
I need that if 1.0 nothing happens,if 1.1 it becomes 1.6, if 1.2 it becomes 1.12, if 1.3 it becomes 1.18 etc... The problem is that this trick doesn't work for 1.2!I don't know why it writes 1.7! and also 1,4 it writes 1,28 and not 1,24! Thanks so much

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