Can someone show me a simple example of how to pass a range of cells
to a UDF and then how to address them in the UDF?

Suppose I have two rows of paired parameters (X and Y)

A B C D
1 X X1 X2 X3
2 Y Y1 Y2 Y3

I need to write a regression function that will operate on the pairs
from column B to successive columns to the right.

I understand that I can pass a range to a UDF something like this:

A B C D
1 X X1 X2 X3
2 Y Y1 Y2 Y3
3 f(x,y) =F(B1:B1,B2:B2) =F(B1:C1,B2:C2) =F(B1:D1,B2:D2)

Suppose I wanted to compute the sum of the product pairs (X1*Y1),
(X1*Y1 + X2*Y2), (X1*Y1 + X2*Y2 + X3*Y3), ...

What would the VBA code look like? My function is a lot more
complicated than that and involves looping, but if I had the code for
this simple sum of products, I could adapt it.

Thanks