Function of vector with meshgrid and surf

[karl]

I have a small problem with the syntax.

I have a function "frame" which I don't want to change since it is used in this 
form in other functions:

function fr = frame (x)
fr=x(1,:)+x(2,:);
endfunction

Now, when I want to plot the function as surface, I tried:

x1=0:0.1:1;
[X,Y]=meshgrid(x1,x1);
Z=frame([X,Y]); #<- not ok I tried different variants but all do not work
surf(X,Y,Z); #<- error message

How do I have to modify the line "Z=frame([X,Y])" that the surf command works 
and gives the surface?

Thanks
Karl