1. A method for providing alternative computational results in a computer-implemented model, comprising: representing data in the computer-implemented model with a plurality of cells; for each cell, providing a plurality of formulas indicating alternative values of the respective cell; arranging the plurality of formulas for the plurality of cells into a plurality of layers each including no more than one formula for each cell, wherein the plurality of layers are arranged in an ordered set; selectively enabling and disabling the plurality of formulas for the plurality of cells on a layer-by-layer basis; and operating the computer-implemented model, including, for at least one of the plurality of cells, computing, by the computer-implemented model, a value for a formula in an enabled layer to produce a first computational result, and applying, by the computer-implemented model, the first computational result to a formula for the same cell in another enabled layer to compute a second computational result based upon the first computational result.