HOW TO WRITE THE FUNCTION FOR ODE45

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wan rabiatul adawiyyah
编辑： darova 2020-7-8
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);

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采纳的回答

madhan ravi
madhan ravi 2020-7-8
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
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madhan ravi
madhan ravi 2020-7-8
How’s this related to the question you originally asked?? First you asked about ode45() and now a loop?
wan rabiatul adawiyyah
wan rabiatul adawiyyah 2020-7-8
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

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