# Definiing two functions (mathematica)

1. Feb 25, 2012

### rbnphlp

I need to define two functions for a molecule with speed s.
a)it has a horizontal velocity between -s and s
b) v , the vertical velocity between +Sqrt[s^2-u^2] and -Sqrt[s^2-u^2]

This is what I have done
for a)
Code (Text):
f[s_]:=RandomReal[{-s,s}]
for b)
Code (Text):
g[s_,u_]:=RandomReal[{-Sqrt[s^2-u^2],+Sqrt[s^2-u^2]}]
now , If I enter f[2] I get u, so I have s and u from first code. How do I use these values in the second code (without manually inputting them)?

Thanks a bunch

2. Feb 25, 2012

### jackmell

You mean just

g[s,f] ?

3. Feb 25, 2012

### rbnphlp

Yes ,thats what I want ..But how do I put into mathematica ?

If just insert what you have written I get

RandomReal::unifr: "The endpoints specified the uniform distribution range are not real valued

I also Tried,

Code (Text):
g[s_] := RandomReal[{-Sqrt[s^2 - f[s]^2], +Sqrt[s^2 - f[s]^2]}]
However , what it does in this case is , finds f for -Sqrt[s^2 - f^2] and +Sqrt[s^2 - f^2] seperately , so I get different f in that case..

Any ideas?

4. Feb 25, 2012

### jackmell

I believe that's because the arguments to RandomReal have to be real. But for example if I entered:

g[2,f[3]]

the argument passed to Sqrt results in a complex number. Either need to make sure s^2-u^2 is real or either use RandomComplex.