 Yearstretch GASolver Reference
 Model Creation

How to build a worksheet model for GASolver

GASolver is good at solving values for models created with Excel work sheets. A GASolver model is the same as any other Excel work sheet model although some care needs to be exercised in arranging the layout of the working cells within the work sheet. Models must have inputs and an output and may also have optional intermediate calculation cells.

Models may describe anything that one can define within an Excel work sheet. GASolver will try to find values for the model that lead to some predefined answer.

The Input Cells

Inputs are those cells that GASolver may change in order to find a solution. In the model A = B * C + D where we are looking for a suitable A, the inputs we must change are B and C and D. The cells that hold values for B and C and D are therefore Input Cells.

GASolver requires that all the input cells are placed in one contiguous vertical block within a single column.

 Input cell pattern OK? Yes No No No

It does NOT matter to GASolver what order the input cells are placed within the block.

 Input cell pattern OK? Yes Yes

Input range

GASolver will try out different values in each of the input cells during its search for the best solution to your model. If your input values can assume any number possible then GASolver will have to try out samples from an almost infinite range of possibilities. This takes time. In order to speed up the solution process, or to ignore invalid solutions to a particular model, you may set a range of allowed numbers for each input cell. See Input Cell Value Range. An input cell block may have a constrained input cell value range.

The Output Cell

The Output is the cell containing the answer to the model, function or formula that GASolver is to solve by changing the input cells. In the model A = B * C + D, the output is A. The cell that holds the value for A is therefore the Output, or Target Cell.

You may place the output cell anywhere within the worksheet that contains your input cells. Output values

GASolver will create sample output values anywhere within the range allowed by the input cell ranges and your model, function or formula. In order to ignore invalid solutions to a particular model, you may set constraints on the values allowed for your output cell. See Adding Constraints. An output cell may have a constrained value range.

Single Cell Result

Your model must result in a value placed into a single cell. GASolver cannot solve a model with multiple result cells. GASolver will find a solution for a model where the single result cell is required to be as large as possible (where 10,000 would be a better solution than 5,000), as small as possible (where 0.1 is a better answer than 123) or is equal to some defined specific value (23.5).

Intermediate Cells

In many complex models some cells are used to hold the results of intermediate calculations. In the example A = B * C + D one might introduce an intermediate cell that holds the result of B * C. You may place intermediate cells anywhere within the worksheet that contains your input cells.

Intermediate values

Intermediate calculations do not play a direct part in the GASolver process (the results of the intermediate cells are later fed through to the output cell). However, in order to ignore invalid solutions to a particular model, you may set constraints on the values allowed within intermediate cells in the same way as constraints can be placed on the Output cell value. See Adding Constraints. An intermediate cell may have a constrained 'output' value range.

Performance Point: Output cell constraints or Input cell limits? It is useful to appreciate the difference as limiting the input cell values is far faster than constraining the output cell values. Although there is no technical reason why you should not use 'output' constraints to limit 'input' cell values we strongly recommend that, where possible, you use constraints only on output cells and limit input cell values by the method provided.

See Also Using Constraints, Input Cell Value Range, Using Constraints, Sample 1, Sample 2, Sample 3.