Solver FAQs - General Questions

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What is the Solver?
What can I do with the Solver?
What kinds of models can the Solver handle?
How large can my Solver models be?
How long will it take for the new Solver to find an answer?
Are there any examples of Solver models that I can use?
How will I obtain technical support for the new Solver?

What is the Solver?

The Solver is a what-if analysis tool. It automatically finds the optimal values for certain input cells, called decision variables, which drive a spreadsheet model. The solver ensures that these values satisfy limits, called constraints, on other cells calculated by formulas in the model. A designated formula cell, called the objective, is maximized or minimized at the optimal solution. The new Solver for 1-2-3 97/98 was developed by Frontline Systems Inc.

What can I do with the Solver?

You can use the Solver for a wide variety of problems, but the most common ones involve the allocation of scarce resources. The resources may be raw materials, people or equipment time, money, or anything else in limited supply. The decision variables represent the amounts of resources, and the constraints quantify the limits on their use. The Solver finds the allocation of resources that will maximize profit or minimize cost, while satisfying the constraints.

What kinds of models can the Solver handle?

The Solver can handle models containing both linear and smooth nonlinear functions of the variables. Examples of linear functions are @SUM(A1..A3) and +A1+B1*A2-C1*A3 where A1..A3 are decision variable cells, and B1 and C1 are constant in the problem (it's OK if they contain formulas that don't depend on the variables). Examples of smooth nonlinear functions are +A1^2, +A1*A2 and @COS(A1).

The Solver usually has trouble with models containing discontinuous functions of the variables. These are functions whose graph contains a sudden break or jump in value. Examples are @IF(A1,2*A1,4*A1) as well as @CHOOSE and @LOOKUP functions involving decision variables. However, an @IF whose first argument does not depend on any of the variables is OK in a Solver model.

The new Solver also supports integer constraints, which force some or all of the decision variables to be whole numbers at the solution. You can use integer constraints to handle fixed costs and yes/no decisions, and to express some conditions that would otherwise require @IF or @LOOKUP.

How large can my Solver models be?

The new Solver handles models with up to 200 decision variables. Linear models can have any number of constraints; nonlinear models may have up to 100 constraints, in addition to simple bounds on the variables. There is no limit on the number of cells that can participate in the calculation of the objective and constraints, or on the complexity of the formulas they contain. As a practical matter, the new Solver can handle substantially larger problems than the old one. If you need to solve problems of more than 200 decision variables, Frontline Systems offers enhanced versions of its Solvers that can handle as many as 16,000 decision variables. Explore this Web site, or call Frontline Systems at (702) 831-0300 for more information.

How long will it take for the new Solver to find an answer?

This will vary significantly depending on the size and complexity of your model, whether it is linear or nonlinear, and whether it includes any integer constraints. On most common problems, the new Solver is much faster than the old one. Solutions to all-linear models can be found much faster than nonlinear models of equivalent size. If your problem contains integer constraints, the Solver may take a long time, since it must solve many variants of the model, each one a linear or nonlinear subproblem.

Are there any examples of Solver models that I can use?

Yes. The new Solver comes with an example workbook SOLVSAMP.123, which includes seven worksheets containing predefined Solver models. The examples include Product Mix, Shipping Routes, Staff Scheduling, Cash Management, Portfolio Optimization and Engineering Design. Many more examples will be available soon on this Web site.

How will I obtain technical support for the new Solver?

Free electronic support, including online documentation and answers to common questions from 1-2-3 users, will be available on this Web site. In the next few months, we will be adding many example models, and a Solver discussion group to this site. Fee-based telephone technical support will be available from Frontline Systems at (702) 831-0300, or via fax to (702) 831-0314.

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