[TRNSYS-users] calculation error?

Stefan de Kool S.deKool at chri.nl
Wed Mar 28 07:11:39 PDT 2007


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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TIME        	c20         	c10         	c0          	teller      	noemer      	c_pred    
+0.00000E+00	+6.00000E+02	+5.61500E+02	+3.00000E+02	+1.35282E+05	+2.23000E+02	+6.06647E+02
+1.00000E+00	+6.09000E+02	+5.70485E+02	+3.11550E+02	+1.35719E+05	+2.20420E+02	+6.15730E+02
+2.00000E+00	+6.18000E+02	+5.79470E+02	+3.23100E+02	+1.36110E+05	+2.17840E+02	+6.24815E+02
+3.00000E+00	+6.27000E+02	+5.88455E+02	+3.34650E+02	+1.36454E+05	+2.15260E+02	+6.33902E+02
+4.00000E+00	+6.36000E+02	+5.97440E+02	+3.46200E+02	+1.36751E+05	+2.12680E+02	+6.42991E+02
+5.00000E+00	+6.45000E+02	+6.06425E+02	+3.57750E+02	+1.37003E+05	+2.10100E+02	+6.52082E+02
+6.00000E+00	+6.54000E+02	+6.15410E+02	+3.69300E+02	+1.37207E+05	+2.07520E+02	+6.61176E+02
+7.00000E+00	+6.63000E+02	+6.24395E+02	+3.80850E+02	+1.37366E+05	+2.04940E+02	+6.70272E+02
+8.00000E+00	+6.72000E+02	+6.33380E+02	+3.92400E+02	+1.37477E+05	+2.02360E+02	+6.79371E+02
+9.00000E+00	+6.81000E+02	+6.42365E+02	+4.03950E+02	+1.37543E+05	+1.99780E+02	+6.88472E+02
+1.00000E+01	+6.90000E+02	+6.51350E+02	+4.15500E+02	+1.37562E+05	+1.97200E+02	+6.97575E+02
+1.10000E+01	+6.99000E+02	+6.60335E+02	+4.27050E+02	+1.37534E+05	+1.94620E+02	+7.06682E+02
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+1.30000E+01	+7.17000E+02	+6.78305E+02	+4.50150E+02	+1.37340E+05	+1.89460E+02	+7.24903E+02
+1.40000E+01	+7.26000E+02	+6.87290E+02	+4.61700E+02	+1.37173E+05	+1.86880E+02	+7.34018E+02
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