[TRNSYS-users] calculation error?

[Stefan de Kool]

Dear all,

 

I'm having a problem with a simple calculation (see attached files). I have
3 inputs, c0, c10 and c20, which are defined by type 14. I run the following
calculation:

 

c-pred= teller / noemer, with teller = (c10^2 - c0*c20) and noemer = (2*c10
- (c0+c20)). 

 

When I output these values, I get strange differences compared to values
calculated in XL (see attached xl-file). At the first 48 timesteps
everything goes fine with relative errors on the order of 10^-6, but from
the 49th step on, errors on the order of 10^-4 occur. Strangly these occur
only at the uneven timesteps. The errors occur only in teller and noemer but
are, I suppose, levelled out after division.

 

Can anyone help with this? I suspect it has something to do with
rounding-off errors but I can not find the exact cause. The only change I
see in the input values at step 49 is that c10 changes from below 10^3 to
above 10^3.

 

I tried decreasing the tollerances and also using Powell instead of
Succesive, to no avail. When I change the timebase from 100h to 1000h (also
for the type 14), the errors occur at different timesteps and different
rates.

 

Thanks in advance,

Stefan de Kool 

 

Cauberg-Huygen Raadgevende Ingenieurs B.V.

Bezoekadres: Boterdiep 48, 3077 AW  ROTTERDAM

Postadres: Postbus 9222, 3007 AE  ROTTERDAM

Telefoon: +31 (0)10-2443638

Fax: +31 (0)10-425 44 43

http://www.chri.nl

 



 

 

 

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