Bugfixing for ode45 - "Too many input arguments"

Hey,

I am currently trying to solve a first order ODE using matlab's ode45. Here is my code:

function [ y ] = kepEQ( in )
%KEPEQ Function for ode45

y = zeros(4,1);
y(1) = in(2);
y(2) = - in(1) / (in(1)^2 + in(3)^2)^(3/2);
y(3) = in(4);
y(4) = - in(3) / (in(1)^2 + in(3)^2)^(3/2);

end

and then I call ode45 using

out = ode45(@kepEQ, [0 steps*dt], [qStart(1) pStart(1) qStart(2) pStart(2)]);

All used variables (steps, dt, qStart and pStart) have been initialized correctly, all are scalar values (well, at lest qStart(1) etc. are scalars). The error message produced by this code is:

??? Error using ==> kepEQ
Too many input arguments.

Error in ==> odearguments at 109
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.

Error in ==> ode45 at 173
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...

I can't really follow this error message and don't know, why it should have too many input arguments. Any help is appreciated :)

Answer 1

[Sean de Wolski]

If you look in the doc for ode45 and all of the other ode solvers it shows that they need to recieve two inputs (t and y) (even if your function doesn't need both inputs).

Thus for yours, it might look like

function [ y ] = kepEQ( junk , in ) 
  %stuff
end

[Rohan Walia]

This was really helpful! Thank you!

[Stephen23]

Since R2009b the recommended syntax has been to use tilde to indicate unused input arguments:

function y = kepEQ(~,in)
%                  ^ ignore first input argument, if provided.

https://www.mathworks.com/help/matlab/matlab_prog/ignore-function-inputs.html

https://blogs.mathworks.com/loren/2009/09/11/matlab-release-2009b-best-new-feature-or/