differential equations

I wanna solve this differential equation.

lambda is function for w.

This is my script.

clear

clc

syms w(x) lambda Eox

%% set constant

kb = 8.617343*(10^-5); % Blotzmann constant [eV/K] %%1.38066*10^(-23) %%[J/K]

T = 300; %%Temperature [K]

q = 1.60218*(10^-19); % charge [C]

w0 = 1.5*kb*T; %%[eV]

n = 1.3 ;%How fast the value of 'lamda' decreases for higher average electron energies

A1 = 10.4314 * 10^-9;

A2 = 11.1765 * 10^-9;

%% boundary condition

w_max = 2; %%[eV]

lamda_min = 0.5 * 10^-9; %[m]

lamda_max = 7.5 * 10^-9; %[m]

%% relaxation length depending on average energy

lambda = piecewise(w<=w_max,(A1)*(w^n)*exp(-n*w/w_max) + lamda_min, w>w_max,(A2)*(w^n)*exp(-n*w/w_max));

%% solve ODE

ode = diff(w,x) == Eox - ((w-w0)/lambda);

cond = w(0) == w0;

ysol(x) = dsolve(ode,cond)

And this is error content...

다음 사용 중 오류가 발생함: mupadengine/feval_internal

Invalid equations.

오류 발생: dsolve>mupadDsolve (334번 라인)

T = feval_internal(symengine,'symobj::dsolve',sys,x,options);

오류 발생: dsolve (203번 라인)

sol = mupadDsolve(args, options);

오류 발생: ODE (29번 라인)

ysol(x) = dsolve(ode,cond)

help me plz....

I tried replacing lambda with a constant. Then It works. But I want to keep the lambda as a function for w.

My final goal is to draw a w-Eox graph.

Answer 1

[Manikanta Aditya]

Hi

As per my understanding, when you are trying to solve the differential equation, you are getting an error ‘mupadengine/feval_internal Invalid Equation’.

The ‘dsolve()’ doesn’t provide the functionality to provide that as an input argument to the function.

You can check the following MATLAB Answer to resolve the error:

• https://www.mathworks.com/matlabcentral/answers/498318-error-using-mupadengine-feval-line-187-invalid-equations

Please refer to the following documentation for more info on:

• dsolve() function: https://www.mathworks.com/help/symbolic/dsolve.html

I hope this resolves the issue you were facing.