[Date Index]
[Thread Index]
[Author Index]
Re: Delay Differential Equations
*To*: mathgroup at smc.vnet.net
*Subject*: [mg105227] Re: [mg105198] Delay Differential Equations
*From*: Yun Zhao <yun.m.zhao at gmail.com>
*Date*: Wed, 25 Nov 2009 02:30:55 -0500 (EST)
*References*: <200911241048.FAA00661@smc.vnet.net> <4B0C33E2.5070102@wolfram.com>
Hi Daniel,
Thanks for your reply. But my question is I was trying to solve an
equation, and the solution just doesnt make much sense, and I looked in the
help files, but they didn't really help me much. The problem is this:
I have some cells of type A, and at some point in time, cells of type A are
going to slowly change into cells of type B. So, population size of cell
type A will decrease over time due to two factors: (1) becoming cells of
type B and (2) dying over time. So for a differential equation, i have two
rates, one is the transformation rate (0.0367), one is the death rate
(0.0123). But I want to delay the transformation by 37 hours. So from time
= 0 to time = 37, all that is changing in cells of type A is that they are
dying at the death rate, then after 37 hours, they are also disappearing at
the transformation rate.
So my differential equation is like this:
*solrandom1=NDSolve[{p'[t]**==0.0367*p[t-37]-0.0123*p[t],p[t/;t<0] 30000},p,{t,0,120}]*
What I expect when I plot p(t) over t is a gradual decrease from t=0 to
t=37. Then more decrease from t=37 to t=120. p(t) should never be less
than zero. But when I ran that code in Mathematica, and plotted it using
this command
*Plot[Evaluate[p[t]/.solrandom1],{t,0,120},PlotRange**=EF=82=AEAutomatic]*
p(t) was actually less than zero. I am not able to figure out why this is.
Please tell me what I did wrong. Thanks.
On Tue, Nov 24, 2009 at 1:28 PM, Daniel Lichtblau <danl at wolfram.com> wrote:
> Yun Zhao wrote:
>
>> Hi,
>>
>> Does anyone have experience working with delay differential equations in
>> Mathematica 7? I found some help files on wolfram and Mathematica help,
>> but
>> the information available there were very limited. If anyone can refer me
>> to
>> other online or textual sources, I would really appreciate it. Thank you
>> very much.
>>
>> Mike
>>
>
> Not sure what you saw in the Documentation Center. These are perhaps the
> most useful, worth checking if you have not encountered them already.
>
> howto/SolveDelayDifferentialEquations
> tutorial/NDSolveDelayDifferentialEquations
>
> Daniel Lichtblau
> Wolfram Research
>
Prev by Date:
**Re: Changing variables within a differential equation**
Next by Date:
**Re: Solving systems of differential equations**
Previous by thread:
**Delay Differential Equations**
Next by thread:
**Re: Delay Differential Equations**
| |