How to write function correctly - matlab

Question

I'm making a Matlab program for cell growth,
I have a problem with some function in main.m and I found some functions that I thought are written wrong way:
function y = f(c)
y = 0.5*(1-tanh(4*c-2));
function y = h(c)
y = 0.5*f(c);
function y = g(c)
global beta
y = beta*exp(beta*c);
%y=1+0.2*c;
main.m
%%main program
clear; clc;
global alpha beta gamma
%set parameter values
alpha = 0.9; beta = 0.5; gamma = 10;
dx = 1; X = 210; dt = 0.04; T = 16;
c0 = 1;
%set up arrays
x = [dx:dx:X]; Nx = round(X/dx); Nt = round(T/dt);
p = zeros(1,Nx); nextp = zeros(1,Nx);
q = zeros(1,Nx); nextq = zeros(1,Nx);
n = zeros(1,Nx); nextn = zeros(1,Nx);
u = zeros(1,Nx); v = zeros(1,Nx); r = zeros(1,Nx); c = zeros(1,Nx);
P = zeros(Nt,Nx); Q = zeros(Nt,Nx); N = zeros(Nt,Nx);
%set initial values
p = exp(-0.1.*x);
function y = f(c)
y = 0.5*(1-tanh(4*c-2));
function y = h(c)
y = 0.5*f(c);
function y = g(c)
global beta
y = beta*exp(beta*c);
%y=1+0.2*c;
%start FDM time-stepping
for k=1:Nt
r = p + q;
c = (c0.*gamma./(gamma+p)).*(1-alpha.*(p+q+n));
for i=2:Nx-1
u(i)=((p(i+1)-p(i-1))*r(i)*(r(i+1)-r(i-1))+ 4*p(i)*r(i)*...
(r(i+1)-2*r(i)+r(i-1))-p(i)*(r(i+1)-r(i-1))^2)/(2*...
(dx*r(i))^2);
v(i)=((q(i+1)-q(i-1))*r(i)*(r(i+1)-r(i-1))+ 4*q(i)*r(i)*...
(r(i+1)-2*r(i)+r(i-1))-q(i)*(r(i+1)-r(i-1))^2)/(2*...
(dx*r(i))^2);
end
nextp=p+dt.*(u+g(c).*p.*(1-(p+q+n))-f(c).*p);
nextq=q+dt.*(v+f(c).*p-h(c).*q);
nextn=n+dt.*(h(c).*q);
p=nextp;
q=nextq;
n=nextn;
P(k,:)=p; Q(k,:)=q; N(k,:)=n;
end
figure(1)
for n=1:500:Nt
plot(P(n,:),'LineWidth',1.2); hold on;
end
axis([0 270 0 0.6]);
figure(2)
for n=1:500:Nt
plot(Q(n,:),'LineWidth',1.2); hold on;
end
axis([0 270 0 0.6]);
figure(3)
for n=1:500:Nt
plot(N(n,:),'LineWidth',1.2); hold on;
end
axis([0 270 0 1]);
animation.m
%create image for cells
rand('state', sum(100*clock));
prefix='t';
Nm=0;
figure(1)
for n=1:250:Nt
Nm=Nm+1;
for i=1:Nx
tP=round(P(n,i)),tQ=round(Q(n,i)),tN=round(N(n,i));
for m=1:tP
theta=2*pi*rand();
plot(i*sin(theta),i*cos(theta),'b.'); hold on;
end
for m=1:tQ
theta=2*pi*rand();
plot(i*sin(theta),i*cos(theta),'r.'); hold on;
end
for m=1:tN
theta=2*pi*rand();
plot(i*sin(theta),i*cos(theta),'k.'); hold on;
end
axis square
axis([-300 300 -300 300])
end
print('-djpeg','-r100',sprintf('%s_%s',prefix,num2str(Nm)));
end
clear MM
for i=1:Nm
[XX,map]=imread(sprintf('%s_%s',prefix,num2str(i)),'jpeg');
imagesc(XX);
MM(i)=getframe;
pause(0.1);
end
Please help me solve this problem..

Answer 1

You're main.m is a script, not a function (it doesn't start with the word function), see function and Scripts vs. Functions).
In short: function declaration is not allowed in command-line or scripts only in function files.
Do as oro777 advises,
create a seperate file for each function.
Another way is to turn your main.m into a function too, by starting it with function main. Then decleration of additional functions is allowed in the same file, but these are all local functions which means they will only be available from within that file. You can not call them from outside the file they were declared in.

Answer 2

You should write the output error so we can see which function is badly written. At first view, I would say you should use longer function names because with only one letter, it may easily shadow with a variable name and I would advise not to use global variables.
I see that your functions are defined in the same file as the main program, I would advise to create one function per file. For example a f_function m-file with the following code.
function y = f_function(c)
y = 0.5*(1-tanh(4*c-2));
Do the same for your two other functions and place your newly created m-files in the same folder as your main program.