# Rounding using 'fix'... possibly a bug?

5 views (last 30 days)
Commented: Brad on 15 Oct 2013
Could someone tell me if this is a bug, or is there some logical reason 'fix' would round:
.3/.1 = 2
whereas
.4/.1 = 4
K>> fix(.3/.1)
ans =
2
K>> fix(.4/.1)
ans =
4
K>> fix(.7/.1)
ans =
6
K>> fix(.5/.1)
ans =
5
Jan on 14 Oct 2013
It is such surprising that the well known floating point effects appear for beginners usually for the value 0.3 . Usually it is:
find((0:0.1:1) == 0.3) % replies [] !!!

James Tursa on 14 Oct 2013
To see what is going on you can examine the exact floating point values. Note that none of your original numbers except 0.5 can be represented in IEEE double format exactly:
>> num2strexact(.7)
ans =
0.6999999999999999555910790149937383830547332763671875
>> num2strexact(.5)
ans =
0.5
>> num2strexact(.4)
ans =
0.40000000000000002220446049250313080847263336181640625
>> num2strexact(.3)
ans =
0.299999999999999988897769753748434595763683319091796875
>> num2strexact(.1)
ans =
0.1000000000000000055511151231257827021181583404541015625
>> num2strexact(.7/.1)
ans =
6.99999999999999911182158029987476766109466552734375
>> num2strexact(.5/.1)
ans =
5
>> num2strexact(.4/.1)
ans =
4
>> num2strexact(.3/.1)
ans =
2.999999999999999555910790149937383830547332763671875
You can find num2strexact here:
Thank you James, much appreciated!

Image Analyst on 14 Oct 2013
Looks like another case explained by the FAQ.