Re: strange problem

[Gerald Ebberink]

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It is not just representation. This was hust one in a series of 4000
matrix multiplications in a script. It gave me the problem of a
impossible answer,a negative distance in a optical system (this is
possible just not in the system I'm building).

So one of the problems is this number is negative.

Also this problem strikes me as a problem early calculators had.
you know the 1/3 * 3 =0.99999999 problem.

then there is a third thing I would like to point out.

as you can see in your own example -1/100 = -0.01 and not
- -0.01000000000000000020817 which would give you the 2.0817e-17


Geraint Paul Bevan wrote:
| Gerald,
|
| just to follow up to my earlier answer, if the purposes of your
| calculation are just for demonstration, the command "format bank" will
| set Octave to print only two decimal places; it only changes the
| display, however, not the underlying representation so calculations will
| not be affected.
|
| octave:1> format bank
| octave:2> a = [ 1 , 100 ; 0 , 1 ] * [ 1 , 0 ; -1/100 , 1 ]
| a =
|
| ~    -0.00   100.00
| ~    -0.01     1.00
|
|
| --
| Geraint Bevan
| http://homepage.ntlworld.com/geraint.bevan
|

- --
Ing. Gerald Ebberink
Laser Technician

Kernfysisch Versneller Instituut
Rijksuniversiteit Groningen
Zernikelaan 25
9747 AA Groningen
The Netherlands
tel: +31 50 363 3518
lab: +31 50 363 3588
fax: +31 50 363 4003


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