2nd order differential errors

2021 4 15
1 个回答
更新时间：2021 4 16
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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;

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回答（1 个）

William Rose
William Rose 2021-4-15

0 个投票

@John Masters,
Are you getting an error message? If so, what?
I notice that your dydt is mising a "*" after C.

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John Masters
John Masters 2021-4-15
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
William Rose 2021-4-15
the order of the input arguments to dydt=solver() should be (t,y) not (y,t)
William Rose
William Rose 2021-4-15
编辑：William Rose 2021-4-15
@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.

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