# initial condition vector longer than ODE vector?

2 views (last 30 days)
Will on 18 Apr 2023
Commented: Will on 18 Apr 2023
In my code i have to solve an RCL equation 3 times with the ODE45 command for different values of omega. Upon running the code i get the following error:
OMEGA_1 returns a vector of length 1, but the length of initial conditions vector is 2. The vector returned by OMEGA_1 and the initial conditions vector must have the same
number of elements.
Error in ode45 (line 107)
odearguments(odeIsFuncHandle,odeTreatAsMFile, solver_name, ode, tspan, y0, options, varargin);
Error in ProjQ3B (line 21)
[T,Y]=ode45(@omega_1,tspan,[0;0]);
I am not sure how to proceed with properly defining either the vector or initial conditions to clear the error. Can anyone advise? my full code is below:
clear;clc;close all
a=2;
b=5;
% v0 is now set to 10
v0=10;
% Using a,b to determine rest of variables
R=10*a;
C=0.0001/a;
L=0.01*b;
% omega is set to (0.5, 1, 2)*sqrt(L*C)
omega=0.5*sqrt(L*C);
omega2=1*sqrt(L*C);
omega3=2*sqrt(L*C);
tspan=[0 (40*L)/R];
[T,Y]=ode45(@omega_1,tspan,[0;0]);
function I1=omega_1(t,i)
I1=@(t,i)[i(2);-(R/L)*i(2)-(i(1)/(L*C))+((v0*omega)/L)*(cos(omega*t))];
end
function I2=omega_2(t,i)
I2=@(t,i)[i(2);-(R/L)*i(2)-(i(1)/(L*C))+((v0*omega)/L)*cos(omega2*t)];
end
function I3=omega_3(t,i)
I3=@(t,i)[i(2);-(R/L)*i(2)-(i(1)/(L*C))+((v0*omega)/L)*cos(omega3*t)];
end

Alan Stevens on 18 Apr 2023
Do it like this:
a=2;
b=5;
% v0 is now set to 10
v0=10;
% Using a,b to determine rest of variables
R=10*a;
C=0.0001/a;
L=0.01*b;
% omega is set to (0.5, 1, 2)*sqrt(L*C)
omega=0.5*sqrt(L*C);
omega2=1*sqrt(L*C);
omega3=2*sqrt(L*C);
tspan=[0 (40*L)/R];
[T,Y]=ode45(@(t,i) omega_1(t,i,omega,R,C,L,v0),tspan,[0;0]);
plot(T,Y)
function I1=omega_1(t,i,omega,R,C,L,v0)
I1=[i(2);-(R/L)*i(2)-(i(1)/(L*C))+((v0*omega)/L)*(cos(omega*t))];
end
Will on 18 Apr 2023
Many thanks, works perfectly.

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