error calling a function

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

[Jan]

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.

[Susan Santiago]

Thank you for the advice although what I'm working on is a project in which I was specifically asked to solve this function with this method. I will remember this for the future, though

Answer 1

[Stephan]

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

[Susan Santiago]

That was my issue, thank you! It's my first time using a switch function

[Stephan]

My pleasure

Answer 2

[Ngoc Thanh Hung Bui]

ode45(fMu,tspan,IC)

try ode45(@fMU,...) or ode45('fMU',...) instead

[Susan Santiago]

I tried the first option you suggested and got this message ""fMu" was previously used as a variable, conflicting with its use here as the name of a function or command."