How to input a "sym" type equation into ODE45 to solve first order differential equation?
4 visualizzazioni (ultimi 30 giorni)
Mostra commenti meno recenti
haohaoxuexi1
il 5 Set 2021
Commentato: Star Strider
il 6 Set 2021
% Sample
close all;
clear all;
clc;
syms t tt;
a=1;
b=2;
c=3;
fs_d=50*t^2+60*t^4+70*t^9;
fd_d=diff(fs_d,t);
dTime=1e-6; % time step
Tfinal=timeduration; % time final
zeit=0:dTime:Tfinal; %
% ODE solver
% initial condition
x1_0=0;
dx1_0=0;
%ode45
options = odeset('RelTol',1.e-6);
[tt,dx] = ode45(@(tt,x) Output123(tt, x, a, b, c, fd_d, t), zeit, x1_0, options);
function dx = Output123(tt, x, a, b, c, fd_d, t)
tic;
%dx(1)=x(2);
dx=-a*subs(fd_d,t,tt)*b/(c)-x*(b/(c));
dx = dx'; % output result
toc;
end
The above the a sample code I want to achieve, it is a first order differential equation, the "subs" method works for second order differential equation.
Can anyone help me with this problem?
Thanks,
0 Commenti
Risposta accettata
Star Strider
il 5 Set 2021
I do not understand what you are doing.
However the correct way to use a symbolic different ia equation with the numeric solvers would be something like this —
syms a b c t tt x
fs_d=50*t^2+60*t^4+70*t^9;
fd_d=diff(fs_d,t);
f=-a*subs(fd_d,t,tt)*b/(c)-x*(b/(c))
Output123 = matlabFunction(f, 'Vars',{tt,x,a,b,c})
a=1;
b=2;
c=3;
timeduration = 1;
dTime=1e-6; % time step
Tfinal=timeduration; % time final
zeit=0:dTime:Tfinal; %
x1_0=0;
dx1_0=0;
options = odeset('RelTol',1.e-6);
[tt,x] = ode45(@(tt,x) Output123(tt, x, a, b, c), zeit, x1_0, options);
figure
plot(tt, x)
grid
Make appropriate changes to ger the resullt you want.
.
11 Commenti
Walter Roberson
il 5 Set 2021
Then code it by hand if it is morally important for you.
Reminder: the ode*() functions strictly require that the output is double() or single(), but the output of subs() is always symbolic.
Più risposte (0)
Vedere anche
Categorie
Scopri di più su Symbolic Math Toolbox in Help Center e File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!