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## precision octave vs matlab

 From: michaelschmid1 Subject: precision octave vs matlab Date: Thu, 1 Jun 2006 07:03:50 +0200

```I don't think it's a octave bug. If it's a bug, I think I'm the culprit :-(
The complete algorithm need several hundred lines of code... so I don't think
I will put this here...
I will do some more search and if I will find a position where I don't know
why a difference occurs... I will ask again...
but then with code ...

thanks
michel

| Hi all
|
| First thanks for all the answers about my "global" problem... it works
now...
|
| but now the next problem..
|
| I have programmed some parts of a neural network toolbox for Octave, like
| the one of matlab. Some commands are working like "newff, train, sim" and
| so on..
| For the first training algorithm I decided to realize Levenberg-Marquardt.
| Now if I make a comparison between the results of matlab and octave, there
| are some small differences...
| I searched for calculating errors but can't find anything. As far as I
know,
| both are using double-precision ... so where does this difference come
from?
| Is it really a calculating error or only a "rounding error"?
|
| Octave output:
| ================
| simOut =
|
|  Columns 1 through 8:
|
|   1.67883  2.05781  1.21596  2.82417  2.06661  2.00662  2.99825  1.65494
|
|  Columns 9 through 16:
|
|   1.65087  1.90819  1.90195  1.70142  2.61220  1.99405  0.99050  1.91911
|
|  Columns 17 through 24:
|
|   1.94686  0.93073  1.87499  1.75138  1.71708  2.21930  0.94781  2.02244
|
|  Columns 25 through 30:
|
|   2.01943  1.10781  2.02009  1.85863  2.71098  1.30415
|
| matlab output:
| ==============
|
| simOut =
|
|   Columns 1 through 17
|
|     1.6767    1.9494    1.1277    2.7196    2.0406    1.9435    2.8583

|  1.6444    1.6437    1.8839    1.7769    1.6008    2.7412    1.9360
1.0998
|    1.8426    1.8144
|
|   Columns 18 through 30
|
|     1.0464    1.8657    1.7506    1.6612    2.1693    1.0655    1.8792

|  2.0094    1.0119    1.9947    1.8084    2.5923    1.2365
|
| Of course both programmes have the same initial conditions...
|
| I hope someone have similar experience with this kind of "trouble"
| and that this person can tell me that I didn't make a calculation error..

Given the information you have provided (just the outputs and no code)
how can anyone tell?

If you think you have found a bug in Octave, then please submit a
www.octave.org/bugs.html first to learn how to submit a useful bug
report that provides enough information to allow someone to actually
fix the problem.

Thanks,

jwe

```