error calling a function
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Susan Santiago
le 13 Mai 2018
Commenté : Susan Santiago
le 13 Mai 2018
function f = Mu(t,y,ti,tf,n)
m1 = 55;
m2 = 400;
m3 = 100;
k1 = 230000;
k2 = 30000;
k3 = 50000;
k4 = 3000;
n2 = 1500;
n3 = 4000;
n4 = 700;
tm = (ti+tf)/2;
t1 = tf/4;
L0 = 5;
v = 15;
A = 0.03;
M =[0 1 0 0 0 0;
-(k1+k2)/m1 -(n2+n4)/m1 k2/m1 n4/m1 0 n4/m1;
0 0 0 1 0 0;
k2/m2 n2/m2 -(k3+k2)/m2 -(n3+n2)/m2 k3/m2 n3/m2;
0 0 0 0 0 1;
k4/m3 n4/m3 k3/m3 n3/m3 -(k3+k4)/m3 -(n3+n4)/m3];
switch n
case 1
u = (A/2)*(1-cos(2*pi*v*t/L0));
case 2
u = 1*(t<tm)+(-1)*(t>=tm);
case 3
u = 0*(t<tm)+1*(t>=tm);
case 4
u = 1*(t<tm)+0*(t>=tm);
case 5
u = (A*t)*(t<=tm)+0*(t>tm);
case 6
u1 = A*t;
u2 = A*(t-2*tm);
u = u1.*(t<=tm)+u2.*(t>tm);
case 7
u1 = A*t;
u2 = A*(-t+4*t1);
u3 = A*(-t+3*t1);
u = u1.*(t<=t1)+u2.*((t>=t1)&(t<=2*t1)) +u3.*(t>=2*t1);
case 8
u = A.*((t>=t1)&(t<=2*t1));
vect=[0;-k1*u/m1;0;0;0;0];
f = M*y+vect;
end
here is the main file where i'm trying to call the above function
% initial conditions
IC=[0 0 0 0 0 0];
%initial time
ti=0;
%final time
tf=20;
%interval where the problems can be solved
tspan=[ti,tf];
%function Matrix*Y+u(t)
fMu=@(t,y) Mu(t,y,ti,tf,1);
[t,y]=ode45(fMu,tspan,IC)
The error I'm receiving says "Output argument "f" (and maybe others) not assigned during call to "Mu"." I'm not sure what that means or how to fix it. Please help
2 commentaires
Jan
le 13 Mai 2018
From the view point of numerical maths it is a professional blunder to use ODE45 to integrate a non-smooth function. See http://www.mathworks.com/matlabcentral/answers/59582#answer_72047. It is like using a drilling machine to beat a screw into the wall. Of course, it is in afterwards and you get a final number. But you have driven the tool against the specifications and have no control if the result is dominated by rounding errors.
The stable way is to run the integration in steps over the smooth intervals and to use the final value of one step as initial value of the next one.
Réponse acceptée
Stephan
le 13 Mai 2018
Hi Susan,
you should finish your switch case command with an end command.
function f = Mu(t,y,ti,tf,n)
m1 = 55;
m2 = 400;
m3 = 100;
k1 = 230000;
k2 = 30000;
k3 = 50000;
k4 = 3000;
n2 = 1500;
n3 = 4000;
n4 = 700;
tm = (ti+tf)/2;
t1 = tf/4;
L0 = 5;
v = 15;
A = 0.03;
M =[0 1 0 0 0 0;
-(k1+k2)/m1 -(n2+n4)/m1 k2/m1 n4/m1 0 n4/m1;
0 0 0 1 0 0;
k2/m2 n2/m2 -(k3+k2)/m2 -(n3+n2)/m2 k3/m2 n3/m2;
0 0 0 0 0 1;
k4/m3 n4/m3 k3/m3 n3/m3 -(k3+k4)/m3 -(n3+n4)/m3];
switch n
case 1
u = (A/2)*(1-cos(2*pi*v*t/L0));
case 2
u = 1*(t<tm)+(-1)*(t>=tm);
case 3
u = 0*(t<tm)+1*(t>=tm);
case 4
u = 1*(t<tm)+0*(t>=tm);
case 5
u = (A*t)*(t<=tm)+0*(t>tm);
case 6
u1 = A*t;
u2 = A*(t-2*tm);
u = u1.*(t<=tm)+u2.*(t>tm);
case 7
u1 = A*t;
u2 = A*(-t+4*t1);
u3 = A*(-t+3*t1);
u = u1.*(t<=t1)+u2.*((t>=t1)&(t<=2*t1)) +u3.*(t>=2*t1);
case 8
u = A.*((t>=t1)&(t<=2*t1));
end
vect=[0;-k1*u/m1;0;0;0;0];
f = M*y+vect
end
I guess what you wanted is shown above. Like you did it, f only gets a value if n=8.
In your example n=1 - that is the reason for f getting no value.
Best regards
Stephan
2 commentaires
Plus de réponses (1)
Ngoc Thanh Hung Bui
le 13 Mai 2018
Modifié(e) : Ngoc Thanh Hung Bui
le 13 Mai 2018
ode45(fMu,tspan,IC)
try ode45(@fMU,...) or ode45('fMU',...) instead
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