2nd order differential errors

Hi,

I am having issues with ODE45,

My function

function dydt=solver(y,t)

Caller

tspan = [0:0.01:3.12];

thrust=6;

g=9.81;

R=1.3;

m12=4.3;

Answer 1

[William Rose]

@John Masters,

Are you getting an error message? If so, what?

I notice that your dydt is mising a "*" after C.

[John Masters]

Hi Thanks for that corrected that, the list of errors is below

Index exceeds the number of array elements (1).

Error in solver (line 7)

dydt=[y(2);(-g+(thrust-(1/2*Rho*A*C*(y(2)^2))/(M+m12-(m13*Fthrust/I)*t)))];

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 caller (line 13)

[t,y]=ode45(@solver,tspan,[0,0])

[William Rose]

the order of the input arguments to dydt=solver() should be (t,y) not (y,t)

[William Rose]

@John Masters The code works when you fix the (t,y) ordering. By the way, you can specify just the start and end time in [tspan]. YOu don;t have to tell it the time step . That results in a more efficient execution because in that case, ode45() adapts the step size as it goes, as need to achieve a certain level of accuracy. See attached image. When I used you code as is, there were 313 evenly space time steps. When I only specified the start and end

tspan = [0,3.12];

there were 105 unevenly spaced times, with a concentration around the "glitch" (staging, perhaps?). See figure below. Code attached.