What is wrong with my outputs?

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Ethan Wong Yew Hoe 2020-7-31

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评论： Ethan Wong Yew Hoe 2020-8-5

Hey all, I can't seem to find a specific error form my code. It came up with a diagram which doesn't make much sense to me. I'm designing a code that allows an object to home in on a target at given coordinates [5, 5].

What my graph showed was the end point of the object's trajectory to be at [5, -5] for reasons which I can;t seem to find. Attached is an excerpt of my code. Am i using the ode45 wrongly? Or is there a flaw in my syntax in general? My aim is to plot x displacement w.r.t to y displacment for the object launched.

Any tips/helps would be much appreciated, thanks in advance!

%========================= Explanation of code ===========================%
% Get launch angle (theta) from user, then get initial x and y coordinates
% Constants are VELOCITY (v), N, DESIGNATED TIME (Td) 
% Variables are x and y 
% LOS, a, L are always changing, so need to INCLUDE THEM IN A LOOP
% Output will be x and y, ALSO ALWAYS CHANGING
%======================= Get input from user =============================%
theta0 = input('Please input launch angle in degrees: ');
x0 = input('Please enter initial x coordinates: '); 
y0 = input('Please enter initial y coordinates: ');
%=========================== Constants ===================================%
v=1600;
N = 3;                      % Proportionality constant
Td = 30;                    % designated impact time
L = 500;                    % NEED TO DERIVE
I = 205;                    % moment of inertia
targetx= 5; targety = 5;    % I set targetcoordinates as [5, 5]
Rgo_x = targetx - x0;
Rgo_y = targety - y0;
%============== Loop to keep churning out x and y values =================%
    theta = theta0; 
    xspan = [x0 targetx];
    yspan = [y0 targety];
    IC = [0 theta0]; 
    
    while x ~= targetx & y ~= targety
    
        Rgo = sqrt(Rgo_x^2 + Rgo_y^2);                                          % Current range between missle and target
        omega = v/Rgo;
    
        LOS = L/(I*omega);                                                      %L = applied torque, I = moment of intertia of gyroscope, omega = v/Rgo                                                                %LOS rate
        Tgo = (1+ (theta-acosd(Rgo_x/Rgo))/10)*(Rgo/v); 
        a = N*v*LOS - (60*v^5*(Td-Tgo))/(N*v*LOS*(Rgo^3)); 
        theta = a*(Rgo_x)/v^2 + theta; 
        
        [x, y] = ode45(@(x, y)odefcn(x, y, a, v), xspan, yspan, IC);
        Rgo_x = targetx - x;
        Rgo_y = targety - y;
        
    end
%================ Plot x and Y values wrt to angle changes ===============%
figure
grid on
plot(x,y)
xlabel('x displacement (m)');
ylabel('y displacement (m)');

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Uday Pradhan 2020-8-5

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Your while loop will not terminate when both x and y are 5, it will terminate when either x or y becomes 5. With the first execution itself x gets the value 5. You may try

while ~(x == 5 & y == 5)

Also I am not so sure about your arguments list in ode45. You may check the documentation first as the fourth option is for "options" structure array.

Ethan Wong Yew Hoe 2020-8-5

Thanks Uday, I have tried to use your arguments for while loop, still doesnt woork. I'm beginning to suspect that something is off with my ode45 parameters passed. Thanks once again and I will let you all know of any updates (for anyone who is interested)

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