Solving ODE/PDE's in Matlab: Advice for Using pde Function

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Discussion Overview

The discussion revolves around solving a set of partial differential equations (PDEs) using MATLAB's pde function. Participants explore the formulation of the equations, boundary conditions, and the implications of known functions on the solution process.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant presents two PDEs involving functions I(t,z) and N(t,z) and seeks advice on using MATLAB for their solution.
  • Another participant questions the necessity of the first equation if I(t) is already known, suggesting a potential misunderstanding of the problem setup.
  • A clarification is provided that I(t) is known and that the first equation describes how I(t) varies with z, leading to I(t,z).
  • Further clarification is sought regarding the specific nature of I(t), with a participant asking if it refers to I(t,0) or another form.
  • The function I(t) is explicitly defined as I(t) = I_{max}exp(-t^2/T), with the boundary condition I(t,0) = I(t) stated.
  • A participant inquires about boundary conditions for N(t,z), indicating that MATLAB may require such conditions for effective problem-solving.
  • A boundary condition for N(t,z) is proposed: N(t=-∞,z) = 0.

Areas of Agreement / Disagreement

Participants express differing understandings of the relationship between the known function I(t) and the PDEs. While some points are clarified, the discussion remains unresolved regarding the implications of these relationships for solving the equations in MATLAB.

Contextual Notes

There are unresolved aspects regarding the assumptions about the known function I(t) and its implications for the PDEs, as well as the specific requirements for boundary conditions in MATLAB.

Who May Find This Useful

Individuals interested in solving PDEs using MATLAB, particularly those dealing with similar mathematical formulations and boundary conditions in their work.

n0_3sc
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I have two PDE's. One in terms of dz and the other in terms of dt:

\frac{dI(t,z)}{dz}=aI(t,z) + bI^2(t,z) - cN(t,z)I(t,z)
and
\frac{dN(t,z)}{dt}=dI^2(t,z) - eN(t,z)

I know the function:
I(t)

I'd like advice on how to attempt this problem on MATLAB using the pde function. (Matlab's examples are too complex to follow).
 
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I might be able to help given that I know at least a little about diff eq.s in matlab, but first:

you say you know I(t), but in your equations I appears as a function of two variables. And if you know THAT function, then what's the use of the first equation?
 
Because I know I(t) the first equation determines how I(t) varies with z thus giving I(t,z).

I should also mention letters on the rhs "a,b,c,d,e" are constants.
 
I'm still not quite getting it. When you say that you know I(t), do you mean that you know I(t,0) or something like that?
 
Yeah sorry it can be a bit confusing when solving a pde in this way.

Here's what I(t) is:
I(t) = I_{max}exp(\frac{-t^2}{T})

I(t,0) = I(t).

The first ODE modifies I(t) as it varies with z giving I(t,z).
 
Aha. Okay, got it, thanks. Do you have a similar boundary condition for N(t,z)? I don't think MATLAB can do much with it if not.
 
Sure, I can think of this one as being a suitable condition:

N(t=-\infty,z) = 0
 

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