Suppose I have a spreadsheet that performs a complicated calculation,
involving LOOKUP functions, and other structures that are not easily
expressed in a single-cell formula or macro.

I would like to treat the whole sheet as a formula, with one cell as
the input, and another as the output. Then on another sheet, I would
like to use that formula, possibly multiple times with different input
values each time (to generate charts or graphs with the variable input
values for example).

Is there any way to define a spreadsheet as a function in this manner?
If not, is there another way to approach this problem?

Thanks,

Tim.