Why do I get error undefined function or variable?

% 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)' )

[KSSV]

You have to define the variables velocity1 ..did you define those?

[Sudhakar Shinde]

It seems velocity1 & velocity2 variables are not defined.

Answer 1

[Shashank Gupta]

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.