Why do I get error undefined function or variable?

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Kamar Ledgister
Kamar Ledgister 2020-10-9
回答： Shashank Gupta 2020-10-12
% Runge Kutta
h = 0.1;
t1 = 0:h:50;
n = length(t1);
v1 = zeros(1,n);
v1(1)=0;
for i = 1:n-1
k1 = velocity1(t1(i),v1(i));
k2 = velocity1(t1(i)+h/2,v1(i)+0.5*k1*h);
k3 = velocity1(t1(i)+h/2,v1(i)+0.5*k2*h);
k4 = velocity1(t1(i)+h,v1(i)+k3*h);
v1(i+1) = v1(i) + (k1+2*k2+2*k3+k4)*h/6;
if ( abs(v1(i+1))<0 || ~isreal(v1(i+1)) )
tf = t1(i);
break
end
end
vel1_RK4 = v1(1:i);
t1_RK4 = t1(1:i);
h = 0.1;
t2 = 50:h:330;
n = length(t2);
v2 = zeros(1,n);
v2(1) = 10;
for i = 1:n-1
k1 = velocity2(t2(i),v2(i));
k2 = velocity2(t2(i)+h/2,v2(i)+0.5*k1*h);
k3 = velocity2(t2(i)+h/2,v2(i)+0.5*k2*h);
k4 = velocity2(t2(i)+h,v2(i)+k3*h);
v2(i+1) = v2(i) + (k1+2*k2+2*k3+k4)*h/6;
if ( abs(v2(i+1))<0 || ~isreal(v2(i+1)) )
tf = t2(i);
break
end
end
vel2_RK4 = v2(1:i);
t2_RK4 = t2(1:i);
figure
plot (t1_RK4,vel1_RK4,t2_RK4,vel2_RK4)
xlabel( 'Time(s)' )
ylabel( 'Velocity (m/s)' )
title( 'Velocity VS Time using Runge-Kutta' )
legend( 'V1(Before ShutDown)' , 'V2 (After ShutDown)' )
  2 个评论
KSSV
KSSV 2020-10-9
You have to define the variables velocity1 ..did you define those?
Sudhakar Shinde
Sudhakar Shinde 2020-10-9
It seems velocity1 & velocity2 variables are not defined.

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回答（1 个）

Shashank Gupta
Shashank Gupta 2020-10-12
you haven't define some variable in your code. these error occur when compiler trying to access a function or variables and it is not defined. Do check your code and see if all variable are properly declared. From the first look, "velocity" does seems like not defined. check other variable too.

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