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i need solve m*d2x/dt2 + c*dx/dt + k*x= 0 with matlab and I have encountered an error Undefined function or variable 't'. please help me

Asked by Thuan Huynh on 22 Apr 2019
Latest activity Edited by James Tursa
on 22 Apr 2019
function dx = kc(t,x)
global cm km
dx = [-cm*x(1) - km*x(2);x(1)];
tspan = [0 15];
ic = [0 1];
global cm km
m = 20; c(1)=5; c(2)= 40; c(3) = 200; k = 20;
km=k/m;
for n = 1:3
cm = c(n)/m;
[t,x] = ode45('kc',tspan,ic);
plot(t,x(:,2)); grid;
xlabel('time - sec.');
ylabel ('displacement-m');
title('m*(d2x/dt2)+c*(dx/dt)+k*x=0; m=10 kg, k=40 N/m')
hold on
end

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1 Answer

Answer by James Tursa
on 22 Apr 2019
Edited by James Tursa
on 22 Apr 2019

Is this code all together in one file as written above? You need to have your driver code (the code that calls ode45) first, and your derivative function code last or in another file. The ode45 function call should not be inside your derivative function.

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