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From: Burcu on 11 Aug 2010 02:08
Hi everyone,

I have been trying to solve some equation but every time I fail :(. first issue is, I am neither familiar with many of the stuff nor a mathematician. so, i am having really hard time to find out how i am going to solve the equation.

dk/dt = (1/3)* (d^2 k/dx^2) + (2/3*k)*(dk/dx)^2 +(beta/3*gamma*t) - (2*k/3*t)


all I am asking is how to solve this, not the solution. I would love to find a method that I can imply and solve the equation. any help/comment/suggestion/advice will be greatly appreciated.

p.s: i am trying 'pdepe' but get error, could not find the reason for it, keep trying.

Thank you,
Burcu
From: Torsten Hennig on 10 Aug 2010 22:48
> Hi everyone,
>
> I have been trying to solve some equation but every
> time I fail :(. first issue is, I am neither
> familiar with many of the stuff nor a mathematician.
> so, i am having really hard time to find out how i
> i am going to solve the equation.
>
> dk/dt = (1/3)* (d^2 k/dx^2) + (2/3*k)*(dk/dx)^2
> +(beta/3*gamma*t) - (2*k/3*t)
>
>
> all I am asking is how to solve this, not the
> solution. I would love to find a method that I can
> imply and solve the equation. any
> help/comment/suggestion/advice will be greatly
> appreciated.
>
> p.s: i am trying 'pdepe' but get error, could not
> find the reason for it, keep trying.
>
> Thank you,
> Burcu

Just let us see what you have done so far using pdepe.

Best wishes
Torsten.
From: Burcu on 11 Aug 2010 08:38
thank you for this quick reply.

I just discovered about pdepe, and I did not really do something great. I got the examples(sample codes) and change it with my equation.

cozum.m file:
%% cozum of the formula
function [c,f,s] = cozum(x,t,u,DuDx)
c = 1 ;
f = 1*DuDx/3;
s = (2/3*u)*((DuDx)^(2))-(2*u/3*t);%+ (b/3*g*t)

cozumBC.m file:
%% boundary conditions
function [pleft,qleft,pright,qright] = cozumBC(xl,ul,xr,ur,t)
pleft = 1 ;
qleft = 0 ;
pright = 0;
qright = 0;

cozumIC.m file:
%% initial conditions
function u0 = cozumIC(x)
u0 = 1; %ca/ca0;
end

when i use this code it gives "input argument DuDx undefined" error. i am not sure what the problem is.
Thank you for your time.
From: Torsten Hennig on 11 Aug 2010 04:58
> thank you for this quick reply.
>
> I just discovered about pdepe, and I did not really
> do something great. I got the examples(sample codes)
> and change it with my equation.
>
> cozum.m file:
> %% cozum of the formula
> function [c,f,s] = cozum(x,t,u,DuDx)
> c = 1 ;
> f = 1*DuDx/3;
> s = (2/3*u)*((DuDx)^(2))-(2*u/3*t);%+ (b/3*g*t)
>
> cozumBC.m file:
> %% boundary conditions
> function [pleft,qleft,pright,qright] =
> cozumBC(xl,ul,xr,ur,t)
> pleft = 1 ;
> qleft = 0 ;
> pright = 0;
> qright = 0;
>
> cozumIC.m file:
> %% initial conditions
> function u0 = cozumIC(x)
> u0 = 1; %ca/ca0;
> end
>
> when i use this code it gives "input argument DuDx
> undefined" error. i am not sure what the problem is.
>
> Thank you for your time.

I don't know where this error comes from, but one
setting is definitely wrong:
pright = 0;
qright = 0;
in cozumBC will result in an error when executing
the code.
If you want to set du/dx = 0 at x = xright, change
this to
pright = 0;
qright = 1;

Best wishes
Torsten.
From: Burcu on 11 Aug 2010 09:27
:) i was just doing that, thank you so much.
I wish i can run this code, otherwise no way i can solve this equation. i have been trying several books and articles about "how to solve nonlinear pdes" last few weeks, but none of them was helpful ( either i did not understand or the form of equations were different).

could you please let me know if you have some other ideas about error?


Thank you,
Burcu
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