ODE45 help with function (numel(y)=1 error)

Question

Chris 2014-4-15

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/125784-ode45-help-with-function-numel-y-1-error

评论： Chris 2014-4-15

Hello, I am trying to solve a system of ODEs with the following function and solver:

function dy=response_h(t,y)
load('Matrices.mat') %loads the workspace to obtain coefficients
dy=zeros(2,1);
K=Stiff(1,1);
C=C_damp(1,1);
M=M_inertia(1,1);
dy(1)=y(2);
dy(2)=-(K/M)*y(1)-(C/M)*y(2);

The ode45 solver (in the script that the Matrices.mat workspace is from):

[T,Yh]=ode45(@response_h,[0 100],[1 0]);
[T,Ya]=ode45(@response_a,[0 100],[1 0]);
[T,Yb]=ode45(@response_b,[0 100],[1 0]);
plot(T,Yh(:,1))
figure
plot(T,Ya(:,1))
figure
plot(T,Yb(:,1))

The other response functions are identical to response_h only they call out different coefficients from the respective matrices.

The error I am getting:

??? Attempted to access y(2); index out of bounds because numel(y)=1.
Error in ==> response_h at 7
dy(1)=y(2);
Error in ==> odearguments at 110
f0 = feval(ode,t0,y0,args{:});   % ODE15I sets args{1} to yp0.
Error in ==> ode45 at 173
[neq, tspan, ntspan, next, t0, tfinal, tdir, y0, f0, odeArgs, odeFcn, ...
Error in ==> AA554HW1 at 139
[T,Yh]=ode45(@response_h,[0 100],[1 0]);

I am relatively new to these types of MATLAB functions, but I do know that the y(2) element doesn't seem to exist, even though I have the correct number of elements in my I.C. vector. Any help for this would be great. Thanks!

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Answer 1

ragesh r menon 2014-4-15

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/125784-ode45-help-with-function-numel-y-1-error#answer_133396

I don't think there is an error in the m script. But this error is shown because you are defining another "y" probably a local y which is another scalar value. See the data "matrices" which you are loading . I think there could be a scalar y in that