Not enough input arguments

Hi so Im writing a code for plotting a satilite path in 3D. (I use here the 4th order Runge Kutta method) my main file is:

y0=[-6035,-3480,2500,-3.437,6.618,2.523];
tspan=[1 9000];
[t3out,y3out]=RK(ode_function,tspan,y0,100,4);

The RK function is as follows:

function [tout,yout]=RK(ode_function,tspan,y0,h,rk)
i=1;
.
.
elseif rk==4 
  for t=tspan(1):h:tspan(2)
     [k11,k12]=ode_function(y0(i,:));
     ytemp(1:3)=y0(i,1:3)+k11*h/2;
     ytemp(4:6)=y0(i,4:6)+k12*h/2;
     [k21,k22]=ode_function(ytemp);
     ytemp(1:3)=y0(i,1:3)+k21*h/2;
     ytemp(4:6)=y0(i,4:6)+k22*h/2;
     [k31,k32]=ode_function(ytemp);
     ytemp(1:3)=y0(i,1:3)+k31*h;
     ytemp(4:6)=y0(i,4:6)+k32*h;
     [k41,k42]=ode_function(ytemp);
     y0(i+1,1:3)=y0(i,1:3)+1/6*(k11+k21*2+k31*2+k41)*h;
     y0(i+1,4:6)=y0(i,4:6)+1/6*(k12+k22*2+k32*2+k42)*h;
     i=i+1;
  end
  tout=[tspan(1):h:tspan(2)];
  yout=y0; 
end

which outputs a time vector and the y vector which contains position (1:3) and velocity (4:6) components

and calls to the ode function which calculates the needed derivatives as follows:

function [f1,f2]=ode_function(y)
%y is a 1x6 row vector containing position (1:3) and velocity (4:6) components
u=3.98716708*10^5;
R=6378.137;
J=0.0010826267;
r=sqrt(y(1)^2+y(2)^2+y(3)^2);
a=[-3*J*u*R^2*y(1)/2/r^5*(1-5*y(3)^2/r^2),-3*J*u*R^2*y(2)/2/r^5*(1-5*y(3)^2/r^2),-3*J*u*R^2*y(3)/2/r^5*(1-5*y(3)^2/r^2)];
f1=y(4:6);
f2=-u*y/r+a;
end

anyways when i run this there is always an error in the RK function stating:

Not enough input arguments. (on the line beginning with r=)

any solutions to this please?

Answer 1

[Walter Roberson]

[t3out,y3out]=RK(@ode_function,tspan,y0,100,4);

[Andrew Shepherd]

Hell Walter, thanks for replying. However i am still getting the same error even with the added @.

[Walter Roberson]

Nothing else is obvious in the code you posted, but the @ was definitely missing in the line you had.

Could you post the full code?

[Andrew Shepherd]

Here I attached my files

[Andrew Shepherd]

It is the same problem with all 3 rk values in the if statement, and btw the @ didnt change it either way but i realized the code i just posted still has it off.

[Walter Roberson]

Once you change all three references to ode_function in RungeKutta.m then you will run into a different problem.

Your y0 is a vector of length 6, so in your ode_function y will be a vector of length 6. In ode_function you calculate a as a vector of length 3. Then you have

f2=-u*y/r+a;

so you are attempting to add a vector of length 6 and a vector of length 3.