3

I have been experiencing some problems running a certain mathematica file in version 9. I've tracked the problem to a particular sum that I perform. Running the same code in version 8 and 9 I get two different results for this sum. If I then ask mathematica whether the two sums are identical mathematica 8 says that they are whereas mathematica 9 says that they are not.

So: I run the same code in version 8 and 9 and get a different result, if I compare the results version 8 says that they are the same, version 9 says that they are not.

Why would this happen? A bug? Comparison attached below.

```
Chop@FullSimplify[
1.9999999999999996` x0^4 + 3.9999999999999987` x0^2 x1^2 +
2.` x1^4 + 0.3333333333333333` x1^2 x2^2 + (0.857142857142857` x0^2 -
0.699854212223765` x0 x1 + 0.14285714285714285` x1^2) x2^2 +
(0.5238095238095237` x0^2 + 0.11664236870396075` x0 x1 + 0.5873015873015872` x1^2) x2^2 +
(0.5238095238095236` x0^2 + 0.11664236870396079` x0 x1 + 0.5873015873015872` x1^2) x2^2 +
(0.5238095238095237` x0^2 + 0.11664236870396089` x0 x1 + 0.5873015873015872` x1^2) x2^2 +
(0.523809523809524` x0^2 + 0.11664236870396096` x0 x1 + 0.5873015873015872` x1^2) x2^2 +
(0.5238095238095236` x0^2 + 0.11664236870396066` x0 x1 + 0.5873015873015873` x1^2) x2^2 +
(0.5238095238095237` x0^2 + 0.11664236870396083` x0 x1 + 0.5873015873015874` x1^2) x2^2 +
1.9999999999999996` x2^4 ==
1.9999999999999996` x0^4 + 2.` x1^4 + 4.` x1^2 x2^2 + 1.9999999999999996` x2^4 +
6 x0^2 (0.5238095238095236` x1^2 + 0.5238095238095236` x2^2) +
x0^2 (0.857142857142857` x1^2 + 0.857142857142857` x2^2) +
x0 (1.166423687039609` x1^3 - 0.6998542122237649` x1 x2^2) +
2 x0 (-0.19440394783993475` x1^3 + 0.11664236870396069` x1 x2^2) +
x0 (-0.1944039478399347` x1^3 + 0.11664236870396072` x1 x2^2) +
x0 (-0.1944039478399347` x1^3 + 0.11664236870396077` x1 x2^2) +
2 x0 (-0.1944039478399347` x1^3 + 0.11664236870396083` x1 x2^2)]
```

Cheers, David

Do not use

`bugs`

tag. It is only for confirmed by community bugs. – ybeltukov – 2013-10-13T11:43:34.547@Artes I also thought that it is a bug, but

`FullSimplify`

just divide by very small number (it's not forbidden) that produces coefficients like`0.375`

. See also example in my answer. – ybeltukov – 2013-10-13T19:03:06.580@ybeltukov That sounds reasonably, I guess that division is because of

`FullSimplify[... == ...]`

which is allowed. Anyway you should include all those remarks to your answer. – Artes – 2013-10-13T19:11:27.377