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

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M
M on 30 Aug 2014
Commented: M on 2 Sep 2014
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

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Answers (4)

per isakson
per isakson on 30 Aug 2014
Edited: per isakson on 30 Aug 2014
Replace the string
Untitled
by
F
and replace
F := int((42 ....
by
F = int((42 ....
and see
M
M on 1 Sep 2014
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'."
  2 Comments
per isakson
per isakson on 1 Sep 2014
"That didn't solve the problem." &nbsp There are several problems.
M
M on 2 Sep 2014
I already tried the changes below, and the function is still not working

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M
M on 1 Sep 2014
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'."
  2 Comments
Geoff Hayes
Geoff Hayes on 1 Sep 2014
Edited: Geoff Hayes on 1 Sep 2014
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
M on 1 Sep 2014
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?

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per isakson
per isakson on 1 Sep 2014
"'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
  1 Comment
M
M on 2 Sep 2014
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);"

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