HOW TO WRITE THE FUNCTION FOR ODE45

Hi. I am still new in Matlab and i don't know how to write this function for this equation. I know i must use ode45 but i don't know how to write that function coding(for eqn 21 and 22)(I attached with the journal that i referred):

I try to write it but it is have some error, this is how i write:

function dvdt=velocityspinsolver(times,velocities)
dvdt=-g-(Kv/m)*sqrt(v^2+v^2)-Dwv/m;
dvdt=(-Kv/m)*sqrt(v^2+v^2)+Kwv/m; %equation (21)
g=32.174;
K=0.00832;
m=0.59375;
D=0.001452;
w=51;

And this is the error:

Unrecognized function or variable 'g'.

Error in velocityspinsolver (line 2)
dvdt=-g-(Kv/m)*sqrt(v^2+v^2)-Dwv/m;

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 dua (line 44)
        [time,velocities] = ode45('velocityspinsolver',0:.005:5, V0);

Answer 1

[madhan ravi]

 ode45(@velocityspinsolver, [0,10],[1,1])

 function dvdt=velocityspinsolver(t,y)
 y = zeros(2,1);
 vx = y(1);
 vy = y(2);
 g=32.174;
 K=0.00832;
 m=0.59375;
 D=0.001452;
 w=51;
 dvdt = [-g-(K*vx/m)*sqrt(vx^2+vy^2)-D*w*vy/m;
 (-K*vy/m)*sqrt(vx^2+vy^2)+K*w*vx/m]; %equation (21)
 end

[wan rabiatul adawiyyah]

hi can i know this function just write in the same file with other or do in the other file like i do before? because for the other i need to 'called' the function of 'velocityspinsolver' like this:

for theta=0:(pi/90):(pi/2) 
    for speed=150:-5:0 
        V0=[speed*cos(theta) speed*sin(theta)];
        [time,velocities] = ode45('velocityspinsolver',0:.005:5, V0); 
        X = zeros (length(time),2); 
        X(1,2)=height; 
        for i = 1:(length(time)-1) 
            X(i+1,1)=(X(i,1)+(time(i+1)-time(i))*velocities(i,1)); 
            X(i+1,2)=(X(i,2)+(time(i+1)-time(i))*velocities(i,2));
        end

[madhan ravi]

Just copy paste my code in a file called Test.m and simply run it.

[wan rabiatul adawiyyah]

i got this error when i copy your script.I dont why or i need to change like this velocityspinsolver(times,velocity)?:

Error using nargin
Error: File: velocityspinsolver.m Line: 2 Column: 16
Local function name must be different from the script name.

Error in odearguments (line 60)
    if (nargin(ode) == 2)

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

Error in dua (line 44)
        [time,velocities] = ode45('velocityspinsolver',0:.005:5, V0);
 

[wan rabiatul adawiyyah]

When i copy your script i got this result

[wan rabiatul adawiyyah]

But i need to run this function to relate in this script below because i want to know thw trajectory for this projectile.Can u help me

[madhan ravi]

How’s this related to the question you originally asked?? First you asked about ode45() and now a loop?

[wan rabiatul adawiyyah]

Sorry sir because i though the function for 'velocityspinsolver' must be call in this loop. Because i need to get the polynomial graph that refer to the projectile motion. When i run and added with your script in to this loop i also get the linear graph. Soory for my mistaken. Sorry sir because i'm still learning to understand this. Here the loop that have the 'velocityspinsolver':

There's another loop from that journal.

%Initial loop, moves large incriments
q=0; 
for theta=0:(pi/90):(pi/2) 
    for speed=150:-5:0 
        V0=[speed*cos(theta) speed*sin(theta)];
        [time,velocities] = ode45('velocityspinsolver',0:.005:5, V0); 
        X = zeros (length(time),2); 
        X(1,2)=height; 
        for i = 1:(length(time)-1) 
            X(i+1,1)=(X(i,1)+(time(i+1)-time(i))*velocities(i,1)); 
            X(i+1,2)=(X(i,2)+(time(i+1)-time(i))*velocities(i,2));
        end
        findnet=(X(:,1)<dtonet); 
        if sum(findnet)>length(time)
            if X(sum(findnet)+1,2)> netheight 
                b=sum(X(:,2)>0); 
                if (X(b,1)>dtonet) && (X(b,1)<(dtonet+dfromnet)) 
                    q=1; 
                end
            end
        end
        if q==1 
            break
        end
    end
    if q==1 
       break
    end
end