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The following message was posted to: PharmPK
I have a question about writing a defferential equation in the
kinetic basic:
usually the equation is of the form
Sub Deriv (Byval t as double)
DZ1 = -Z1*k12
but how do you write a simular eqation were the expression on
the right has time in it (i.e.)
dz/dt = -k12*z*f(t)
thanks
Barry Koplowitz
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The following message was posted to: PharmPK
Barry,
f(t) is usually the solution to another equation in the system. The
exact syntax depends on the way your de solver works. e.g. in NONMEM
for a 2 cpt model:
DADT(1)=A(2)*K21-A(1)*K12-A(1)*K1O
DADT(2)=A(1)*K12-A(2)*K21
In this case the vector A() contains the solutions to the
differential equations whose derivatives are stored in the vector
DADT(). You can think of A() as being equivalent to f(t).
The DE solver may also allow you access to its integration variable
representing the current time (e.g. it may be called t). In this case
you can directly write your own f(t).
--
Nick Holford, Divn Pharmacology & Clinical Pharmacology
University of Auckland, 85 Park Rd, Private Bag 92019, Auckland, New Zealand
email:n.holford.-a-.auckland.ac.nz tel:+64(9)373-7599x6730 fax:373-7556
http://www.phm.auckland.ac.nz/Staff/NHolford/nholford.htm
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The following message was posted to: PharmPK
There are two ways to do it.
1. You can write the expression, f(t), directly to the differential
equation.
2. You can define an another term, for example, C=f(t),
and define
dim C as double at the beginning of the program
and then in the differential equation, use C instead of f(t)
Regards,
Dan Hirshout
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