Problem when using ODE45

Hey guys! This is my first time using this function, and although I have tried to make it work, the program is not running due to some errors I cannot understand Could any of you please help me?

Here is my main code for the function I am trying to analyze.

function dxdt = nonlinear_quarter(t,x)
w = 0.03*(heaviside(t)-heaviside(t-pi)).*(sin(10*t));
g=9.81;
m1 = 290;
m2 = 59;
k1 = 16812;
k2 = 190000;
b1 = 1000;
alfa=4.515*(10^13);
beta=1;
gama=1.545*(10^9);
tau=(1/30);
Ps=10342500;
A=3.35*(10^(-4));
dxdt=zeros(6,1);
dxdt(1) = x(2);
dxdt(2) = -(k1/m1)*x(1)-(b1/m1)*x(2)+(k1/m1)*x(3)+(b1/m1)*x(4)+(A/m1)*x(5);
dxdt(3) = x(4);
dxdt(4) = (k1/m1)*x(1)+(b1/m2)*x(2)-((k1+k2)/m2)*x(3)-(b1/m2)*x(4)-(A/m2)*x(5)+(k2/m2)*w;
dxdt(5) = -alfa*A*x(2)+alfa*A*x(4)-beta*x(5)+gama*x(6)*sqrt(Ps-x(5)*sign(x(6)));
dxdt(6) = -(1/tau)*x(6)-(1/tau)*((K(1))*x(1)+(K(2))*x(2)+(K(3))*x(3)+(K(4))*x(4)+(K(5))*x(5)+(K(6))*x(6));

This function is then called by the following function:

function [t,x]=call_nonlinear_quarter()
 x0 = [0 0 0 0 0 0]';
 tspan=[0 5]; 
opts = odeset('RelTol',1e-2,'AbsTol',1e-4);
[t,x] = ode45(@nonlinear_quarter, tspan, x0,opts);

After running this second function I get the following mistakes:

Error in nonlinear_quarter (line 21)
dxdt(6) = -(1/tau)*x(6)-(1/tau)*((K(1))*x(1)+(K(2))*x(2)+(K(3))*x(3)+(K(4))*x(4)+(K(5))*x(5)+(K(6))*x(6));

Error in odearguments (line 87)
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.

Error in ode45 (line 113)
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...

Error in call_nonlinear_quarter (line 5)
[t,x] = ode45(@nonlinear_quarter, tspan, x0,opts);

Does anyone knows why that is happenning?

Thank you all very much

Answer 1

[Star Strider]

When I run your code, I get:

Undefined function or variable 'K'.

You need to define your special ‘K’ vector.

[Allan Andre do Nascimento]

Thanks!

[Star Strider]

My pleasure!