code function in MATLAB

[itmr]

hhi everybody

i need to code a simple function in matlab and i have some problems
the function getting 4 variable and supose to plot 4 waves.
if the user press just 2 variables thus the function plots 2 waves.

i try to coded its like

function present_sig[x1,x2,x3,x4]
...

if nargin == 2

plot.......

elsif nargin ==4
plot.......

end

and the i try to operste the function from another m. file
the code is ;

persent_sig[x1,x2,x3,x4]
x1=...
x2=...
x3=...
x4=...

and from somehow it doesnt works good
i et error that thevariables undefined.....


i ill be very happy to any assist

thanks all