ODE 45 not working - not enough input arguments

Hi, I'm having an issue with the code shown below. The main problem is with the ode45 solver and the number of variables involved:

function mdot=sim1(t,p,q)
%
Vm=1;
I1=800;
I2=3200;
R1=4000;
R2=800;
C1=1e-5;
C2=5e-6;
M=0.1;
rp=.02;
Ft=0;
A=3.14159*(rp^2);% area of the piston pushing into hydraulic system
n=Vm*A; %relation between TF from V to Q
I=M;
%
p2dot=(Ft/(1+n^2*(I1/I)))+((R1*n^2*(1/I)*p(2))/(1+n^2*(I1/I)))+((n*(1/C1)*q(8))/(1+n^2*(I1/I)));
q8dot=(n*(1/I)*p(2))-((1/I(2))*p(10));
p10dot=((1/C1)*q(8))-(R2*(1/I1)*p(10))-((1/C2)*q(12));
q12dot=(1/I2)*p(10);
%
mdot=[p2dot;q8dot;p10dot;q12dot];

The function is coupled with this code:

clear all
clc
%
tspan=[0 100];   % Time range, [s]
x0=[0;0;0;0];       % Initial momentum and displacement values
%
[t,x]=ode45(@sim1,tspan,x0);
%
% Plot results

When I try to run the code, these errors pop up:

Not enough input arguments.

Error in sim1 (line 16)

p2dot=(Ft/(1+n^2*(I1/I)))+((R1*n^2*(1/I)*p(2))/(1+n^2*(I1/I)))+((n*(1/C1)*q(8))/(1+n^2*(I1/I)));

Error in odearguments (line 90)

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

Error in ode45 (line 115)

odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

Error in DSCSim1 (line 10)

[t,x]=ode45(@sim1,tspan,x0);

How would I go about trying to fix this? I don't exactly know how many or what input arguments I need in order to make the code run. I also don't understand the error I'm getting in sim1 line 16, or in DSCsim1 line 10. Any help would be greatly appreciated.

[madhan ravi]

Would it be possible to upload the equations in Latex form?

[Zachary Cooper]

I'm not sure how to do that

Answer 1

[James Tursa]

ode45( ) requires that the derivative function handle have the specific arguments (t,y), where y is a single state vector. But you have this signature

function mdot=sim1(t,p,q)

That's three arguments, hence the error.

You need to rewrite the sim1 function with a (t,y) input argument list, and extract your p and q variables from y, which will be a 4-element vector.

[Zachary Cooper]

Thank you!