Why I'm keep getting these errors? Please help!

Question

Nawal 2013-7-31

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/83697-why-i-m-keep-getting-these-errors-please-help

评论： Walter Roberson 2019-1-21

I'm writing a program and I can't finish it because I'm keep getting these error below....

Error using odearguments (line 93)
MY_FUNCTION returns a vector of length 1, but the length of initial conditions vector is 2.
The vector returned by MY_FUNCTION and the initial conditions vector must have the same number of elements.
Error in ode45 (line 114)
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...
Error in p3 (line 10)
[ts,xs]= ode45(@my_function,[0,10],[5,0])

My script file :

function ys = my_function (t,y)
W= 50; % weight in lb.
g= 32.2 ;  % acceleration due to gravity ( ft/s^2) 
theta=(35*pi)/(180) ; % radian 
Mk=0.2; % no units 
L= 12 ;% length in ft.
ys = (( 3 ) *( ( (1-(Mk^2))* g* sin(y(1))) - ( 2*Mk*g*cos(y(1))) + (Mk*((y(2))^2)))) / ( L*(2-(Mk^2)));

And the ode45 part is :

% problem # 3 
W= 50; % weight in lb.
g= 32.2 ;  % acceleration due to gravity ( ft/s^2) 
theta=(35*pi)/(180) ; % radian 
Mk=0.2; % no units 
L= 12 ;% length in ft.
[ts,xs]= ode45(@my_function,[0,10],[5,0])

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Answer 1

Richard Brown 2013-7-31

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https://ww2.mathworks.cn/matlabcentral/answers/83697-why-i-m-keep-getting-these-errors-please-help#answer_93271

The error message says it all.

You're only computing one derivative in my_function. You need to define ys(1) and ys(2), because you refer to y(1) and y(2), and provide two initial conditions. You need to have the same number of derivatives as y values.

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Jan 2013-8-1

+1. Actually all you have answered is a rephrased version of the error message. But you hit the point exactly. The meta-message is a recommendation to read the messages carefully. And especially in the combination with Matlab, this is a very good hint.

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