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Re: ode45 issue: dimension mismatch

From: Tweety
Subject: Re: ode45 issue: dimension mismatch
Date: Tue, 6 Feb 2018 16:11:52 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

Hi, Thanks for the reply. Basically, the equation I am trying to solve is

dx/dt = M*x^m (1-x)^n

The equation describes the reaction kinetics of a specific polymer over
time. M=2.93e-5 is a pre factor, m=0.158 and n=1.26 are exponents which
describe the order of the two parts of a reaction.

I wish it was homework so I could actually speak to others having the
same issue... no.

Kind regards,

Am 06.02.2018 um 15:52 schrieb Carlo De Falco:
> Hi,
>> On 6 Feb 2018, at 12:07, Tweety <address@hidden> wrote:
>> Dear all,
>> For my first time, I am trying to solve a differential equation using
>> ode45. My code looks like this:
>> clear; clc;
>> t = linspace(0,400,401);
>> x0 = [0, 0];
>> function f = dx(x,t)
>> M = 2.933e-5;
>> m = 0.158;
>> n = 1.26;
>> dx = M*x^m(1-x)^n;
>> endfunction
>> [t,x] = ode45(@dx, t, x0);
>> The error I get is a dimension mismatch and I do not understand a
>> mismatch between which parameters.
>> Can this function be solved by ode45 at all or should I use a different
>> solver or bring the function to a different form? If so, which? I
>> appreciate any kind of information.
> There are so many errors in the few lines of code above that it is quite
> difficult to understand what actually is the proble that you are trying to 
> solve, maybe it would be easier to understand what you are trying to 
> accomplish
> if you write in formulas rather than in code.
> Is this some sort of homework? 
> We usually don't solve homework questions on this list, but we do answer 
> specific
> questions about the usage of octave functions.
>> Thanks,
>> Jan
> c.

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