Undefined function 'F' for input arguments of type 'char'.

I am trying to create a function F(t) that is equal to a convolution integral, and then compute theta_n(n+1) by taking the value F(tn). However, I'm getting the error "Undefined function 'F' for input arguments of type 'char'". What's the problem?

function [ theta ] = Untitled( theta_o,omega_o )
nt=5001; %since (50-0)/.01 = 5000
dt = .01; % =H
H=.01;

 theta_n = ones(nt,1);
 theta_n(1)=0; %theta_o

 omega_n = ones(nt,1);
 omega_n(1)=-0.4; %omega_o

 epsilon=10^(-6);
 eta = epsilon*10;

 t_o=0;

 for n=1:4999
    tn=t_o+n*dt;
    F := int((422.11/eta)*exp((5*(4*((eta*t-s-tn)^2)/eta^2)-1)^(-1))*omega, s,tn-(n/2),tn+(n/2))
    theta_n(n+1) = theta_n(n) + h*F(tn);
 end

 end

Answer 1

[per isakson]

Replace the string

    Untitled

by

    F

and replace

    F := int((42 ....

by

    F  = int((42 ....

and see

• function, Declare function name, inputs, and outputs

Answer 2

[M]

That didn't solve the problem. I now get the error "Undefined function or variable 't'." I'll post the updated code here:

 function [ bigTheta_n ] = F( bigTheta_o, bigOmega_o )

 nt=5001; %since (50-0)/.01 = 5000
 dt = .01; % =H
 H=.01;
 l=.05;

 bigTheta_n = ones(nt,1);
 bigTheta_n(1)=bigTheta_o; %theta_o

 bigOmega_n = ones(nt,1);
 bigOmega_n(1)=bigOmega_o; %omega_o
 littleOmega_n = ones(nt,1);

 epsilon=10^(-6);
 eta = epsilon*10;

 t_o=0;

 for n=1:4999
    tn=t_o+n*dt;
    littleOmega_n(n) = bigOmega_n(n) - sin(bigTheta_n(n))*cos(2*pi*tn/epsilon)/(2*pi*l)
    syms s
    F=int((422.11/eta)*exp((5*(4*((eta*t-s-tn)^2)/eta^2)-1)^(-1))*littleOmega_n,s,tn-(n/2),tn+(n/2))
    bigTheta_n(n+1) = bigTheta_n(n) + H*F; %Algorithm 1, pg. 248
 end

 end

I get the error "Undefined function or variable 't'."

[per isakson]

"That didn't solve the problem." &nbsp There are several problems.

[M]

I already tried the changes below, and the function is still not working

Answer 3

[M]

I re-wrote the function as follows:

function [ bigTheta_n ] = Untitled( bigTheta_o, bigOmega_o )
nt=5001; %since (50-0)/.01 = 5000
dt = .01; % =H
H=.01;
l=.05;

bigTheta_n = ones(nt,1);
bigTheta_n(1)=bigTheta_o; %theta_o

bigOmega_n = ones(nt,1);
bigOmega_n(1)=bigOmega_o; %omega_o
littleOmega_n = ones(nt,1);

epsilon=10^(-6);
eta = epsilon*10;

t_o=0;

      function Keta = K(t)
          Keta = (422.11/eta)*exp((5*(4*((t-tn)^2)/eta^2)-1)^(-1))        
      end

      function F = F(t)
          sys s
          F = int(Keta(eta*t-s)*littleOmega_n,s,tn-(n/2),tn+(n/2))
      end

for n=1:4999
    tn=t_o+n*dt;
    littleOmega_n(n) = bigOmega_n(n) - sin(bigTheta_n(n))*cos(2*pi*tn/epsilon)/(2*pi*l);
    F = @(t) int(Keta(eta*t-s)*littleOmega_n,s,tn-(n/2),tn+(n/2));
    bigTheta_n(n+1) = bigTheta_n(n) + H*F(tn)
end

end

However, after running this, I get the error "Undefined function or variable 's'."

Even if I get rid of the line "F = @(t)..." and replace it with the following (and place it below where Keta = K(t) is defined):

function F = F(t, ti, tf)
    F = int(Keta(eta*t-s)*littleOmega_n,s,ti,tf)
end

and then replace the final line of

bigTheta_n(n+1) = bigTheta_n(n) + H*F(tn)

with

bigTheta_n(n+1) = bigTheta_n(n) + H*F(tn, tn-(n/2), tn+(n/2))

I still get the same error "Undefined function or variable 's'."

[Geoff Hayes]

M - please stop using the Answer this question box to further the dialog/conversation, since what you are posting does not solve the original question and will just prove confusing for other readers.

You have changed your code considerably in that you have introduced two local functions F and Keta. Why? What is the purpose of each that you feel you need them now?

And you have assigned the output of a statement to F which is the name of your local function.

Look as well at the body of F - what is

 sys s

?

The error message, Undefined function or variable 's', should be clear. You are trying to use s before it has been defined. Where in your code are you doing that?

[M]

Sorry, I didn't see the 'comment on this answer' until now.

As for "sys s", I thought that would matter for the int function. Even if I remove "sys s", I get the same error. 's' is just a dummy variable, so why do I need to define it?

Answer 4

[per isakson]

"'s' is just a dummy variable, so why do I need to define it?" &nbsp

If you try to define a function, F, see Anonymous Functions and Function Basics, Create functions, including anonymous, local, and nested functions

[M]

I tried

F = @(t) int(@(s) Keta(eta*t-s)*littleOmega_n,s,tn-(n/2),tn+(n/2));

and I still get the messages: "Undefined function or variable 's'.", "Error in Untitled/@(t)int(@(s)Keta(eta*t-s)*littleOmega_n,s,tn-(n/2),tn+(n/2))", "Error in Untitled (line 34) bigTheta_n(n+1) = bigTheta_n(n) + H*F(tn);"