Index issue with using a global variables that are vectors in a function

I have written a function in which two global variables, both vectors with 2 entries, are used:

function TH=THETA(y, z); 
global qv;
global dv;
TH=qv(y) + z*((qv(y))^2)/(1 - (dv(y))*z);

When I call the function, such as with THETA(1, 0.5) or THETA(2, 0.5) , I get the following error:

"Index exceeds matrix dimensions."

I am puzzled by this as the index in question, the first argument of THETA, is 1 or 2, and the vectors in the function both have two entries. What might be the problem?

[Stephen23]

"What might be the problem?"

The decision to use global variables is the problem.

This is a classic example of code using globals: buggy, and hard to debug.

As Doug Hull says: "I have never seen MATLAB code where globals were the right thing to do"

Sadly, beginners keep on insisting on using globals for every little task with more than one workspace, and are then surprised when it turns out to be impossible to understand and impossible to debug.

http://www.mathworks.com/matlabcentral/answers/51946-systematic-do-not-use-global-don-t-use-eval

If you need to pass parameters, then read this:

http://www.mathworks.com/help/matlab/math/parameterizing-functions.html

Answer 1

[Azzi Abdelmalek]

Why are you using global? you can simply write

function TH=THETA(y, z,qv,dv); 
TH=qv(y) + z*((qv(y))^2)/(1 - (dv(y))*z);