Why do I get 'Undefined function or variable'?

3 次查看(过去 30 天)
I'm attempting to run 'ode45' and changed the function file code to include an input vector 'u'. Now I get an error stating that 'u' is undefined. I don't know where to define 'u', since it is defined in the function?
(Undefined function or variable 'u'.)
(Error in ode45_ex>@(t,x)DOF1damped(t,x,u,w,u0,m,k,c,varargin))
the function file is:
function [dx, y] = DOF1damped(t, x, u, w, u0, m, k, c, varargin)
u = [u0*sin(w*t); u0*w*cos(w*t)];
y = [x(1);x(2)];
dx = [x(2) ;((-k/m).*x(1) - (c/m).*x(2) + (k/m).*u(1) + (c/m).*u(2))];
end
the ode file is:
clear
close all
clc
u0 = 1; %amplitude ()
w = 1; %hz
m = 0.85048569375; %kg
k = 356.9085; % N/m
c = 10; %N/m*s
tspan = [0 10];
x0 = [0;0];
[t, x] = ode45(@(t,x)DOF1damped(t, x, u, w, u0, m, k, c, varargin), tspan, x0);
data = iddata(x, t, .1);
plot(t, x);
Thanks for any help

回答(1 个)

Stephan
Stephan 2019-6-18
编辑:Stephan 2019-6-18
If u is calculated inside the function it should not be an input argument of the function. Also delete varargin - no need - results in error, because it is a matlab function already:
u0 = 1; %amplitude ()
w = 1; %hz
m = 0.85048569375; %kg
k = 356.9085; % N/m
c = 10; %N/m*s
tspan = [0 10];
x0 = [0;0];
[t, x] = ode45(@(t,x)DOF1damped(t, x, w, u0, m, k, c), tspan, x0);
data = iddata(x, t, .1);
plot(t, x);
function [dx, y] = DOF1damped(t, x, w, u0, m, k, c)
u = [u0*sin(w*t); u0*w*cos(w*t)];
y = [x(1);x(2)];
dx = [x(2) ;((-k/m).*x(1) - (c/m).*x(2) + (k/m).*u(1) + (c/m).*u(2))];
end
  5 个评论
Ben25
Ben25 2019-6-19
My problem is very similar to the section 'Perform Nonlinear Grey Box Estimation' on this example https://ww2.mathworks.cn/help/ident/ug/estimating-coefficients-of-odes-to-fit-given-solution.html#d117e41137 . I don't see the problem.

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