ode45 Error using odearguments (line 95)

I know this one has been asked before, and I looked through several of those answers. I've been over it and over it and can't see where the solution vector is of lentgh 1. Thanks for the help. The first block of code is my main script. THe second is my ode function called by ode45. Here are the errors I get:

@(T,PRY)PRY_ODE(T,PRY,OMEGA,R,ME,G,IXX,IYY,IZZ) returns a vector of length 1, but the length of initial conditions vector is 6. The vector returned by
@(T,PRY)PRY_ODE(T,PRY,OMEGA,R,ME,G,IXX,IYY,IZZ) and the initial conditions vector must have the same number of elements.

Error in ode45 (line 115)
  odearguments(FcnHandlesUsed, solver_name, ode, tspan, y0, options, varargin);

Error in PRY_main (line 35)
    [t,prydot] = ode45(@(t,pry) pry_ODE(t,PRY,Omega,R,mE,G,Ixx,Iyy,Izz),tspan,PRY);
    
    %% Main script
clc; clear;

% Set initial values

PRY = zeros(1,6);

phi = 0; tht = 0; psi = 0;
wx = 0; wy = 0; wz = 0;
RE = 6357;                              % km - radius of earth
RS = 500;                               % km - orbital altitude
R = RE+RS;                              % km
mE = 5.9722e24;                         % kg
G = 6.6743e-11/1000^3;                         % m^3/kg s^2
Omega = sqrt(G*mE/R^3);                 % rad/s
Ixx = 6; Iyy = 8; Izz = 4;              % kg m^2
tend = (2*pi/Omega)/60;
tspan = [0 tend];
init = [1;5;10;15;20;25];

% for k= 1:6
%     phi =ic(k);
%     tht=ic(k);
%     psi=ic(k);
phi = init(1);
tht = init(1);
psi = init(1);

ic = [phi;tht;psi;wx;wy;wz];

    PRY = [phi,tht,psi,wx,wy,wz];
    [t,prydot] = ode45(@(t,pry) pry_ODE(t,PRY,Omega,R,mE,G,Ixx,Iyy,Izz),tspan,PRY);
    
% end

    %% pry_ODE function file
    
% pry_ODE.m
% myODE function for solver
% PRY = [phi,tht,psi,wx,wy,wz,Omega,R,mE,G,Ixx,Iyy,Izz];

function [t,prydot] = pry_ODE(t,pry,Omega,R,mE,G,Ixx,Iyy,Izz)
    prydot = zeros(size(pry));
    
    phi = pry(1);
    tht = pry(2);
    psi = pry(3);
    wx = pry(4);
    wy = pry(5);
    wz = pry(6);
    
    K = 3*G*mE/R^5;
    X = -R*cos(tht)*cos(psi);
    Y = -R*(cos(psi)*sin(phi)*sin(tht)-cos(phi)*sin(psi));
    Z = -R*(cos(phi)*cos(psi)*sin(tht)+sin(phi)*sin(psi));
    
        
    prydot(1) = (Omega+prydot(3))*sin(tht)+wx;
    prydot(2) = (1/cos(phi))*(-(Omega+prydot(3))*cos(tht)*sin(phi)+wy);
    prydot(3) = (1/(cos(phi)*cos(tht)))*(prydot(2)*sin(phi)-Omega*cos(phi)*cos(tht)+wz);
    prydot(4) = (1/Ixx)*((K*Y*Z-wy*wz)*(Izz-Iyy));
    prydot(5) = (1/Iyy)*((K*X*Z-wx*wz)*(Ixx-Izz));
    prydot(6) = (1/Izz)*((K*X*Y-wx*wy)*(Iyy-Ixx));  
    
    
end

Thank you,

Rick

Answer 1

[Star Strider]

First, specify:

prydot = zeros(6,1);

to create the necessary column vector.

Then, since it is only neccessary for ‘pry_ODE’ to return the vector of derivatives, not the time as well, change the function declaration to:

prydot = pry_ODE(t,pry,Omega,R,mE,G,Ixx,Iyy,Izz)

and your system runs without error.

[Rick Sellers]

Thank you, Star Strider.

[Star Strider]

As always, my pleasure!