Variable Usage in Function File

Unfortunately, I still am not very knowledgeable about using "function" commands in Matlab. As such, I have two questions.

1) In this short script, I want to save vel() so I can plot it at the end. But when the script completes, the variable workspace is wiped clean; thus vel() is gone. How can I retain this variable after script completion?

function vend=velocity1(dt, ti,tf,vi)
t=ti;
v=vi;
n=(tf-ti)/dt;
for i=1:n
dvdt=deriv(v);
v=v+dvdt*dt;
vel(i,1)=v;
end
vend=v;
end

function dv=deriv(v)
dv=9.81-(0.25/68.1)*v^2;
end

2) With the same script above, why does the software give me an error if I add a prefix to it as shown in the following? These input variables need defined, so I'm not sure why the software would give an error.

dt=0.5;
ti=0;
tf=12;
vi=0;

function vend=velocity1(dt, ti,tf,vi)
.
.
.
<same script as above>

Thanks in advance, M Ridzon

Answer 1

[James Tursa]

1) Return vel as an output of your function. E.g.,

function [vel,vend] = velocity1(dt, ti,tf,vi)

2) Have your driver code and function code in separate files. E.g.,

% A file called velocity1_driver.m (or some other name of your choosing)
dt = 0.5;
ti = 0;
tf = 12;
vi = 0;
[vel,vend] = velocity1(dt, ti, tf, vi);
  :
 etc

And then a function file

% A file called velocity1.m
function [vel, vend] = velocity1(dt,ti,tf,vi)
  :
 etc