[TRNSYS-users] Intel 8.1 - MVS2003.NET - differential equation

Jeff Thornton thornton at tess-inc.com
Thu Jan 26 10:07:05 PST 2006

Quoting "Jocelyn.Pacquelet at UTBM.fr" <Jocelyn.Pacquelet at utbm.fr>:

> Also we'd like to know if anybody has already try to solve a differential
> equation with the function called Differential_EQN() (manual programmer's
> guide as the example provided in the manual is not very clear.

I use the Differntial_Eqn function all the time.  There are several important

1) Describe the differential equation in the form:  dT/dt=aT+b  The a and b
terms you calculate (dependent on time, parameters, inputs etc.) will be passed
directly to the function.

2) Provide the initial value of T (TI) as a value to the function (typically
retrieved from the storage array at the beginning of the timestep.

3) Call the function : Call DIFFERENTIAL_EQN(TIME,a,b,TI,TF,TBAR)

4) Record the value of T at the end of the timestep (TF) using the storage

5) After convergence each timestep (Info(13)>0) you'll need to set the final
value of T (TF) as the initial value of T (TI) for the next timestep.

6) All outputs from the model should be based on the average temperature over
the timestep (TBAR) as this is the standard TRNSYS convention for outputs
(averages over the timestep).

If you need me to send you (or to the whole list) a very simple example type
that models a lump of mass for example using the DIFFERENTIAL_EQN function just
let me know.


Jeff Thornton
Thermal Energy System Specialists
2916 Marketplace Drive - Suite 104
Madison WI 53719 USA
Phone: 608-274-2577
Fax: 608-278-1475

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