# Key Benefits of What'sBest!

What'sBest! offers unmatched solution speed, capacity and reliability. The internal linear, nonlinear and integer solvers utilize state-of-the-art techniques, and our dedication to ongoing development will ensure their continued superiority.

**Speed**

When it comes to speed, What'sBest! outperforms stand alone solvers, much less any competing spreadsheet solver. Its commercial quality Linear Programming solver combines with superior Integer Programming technology to set a new standard in optimization speed.

**Capacity**

While competing spreadsheet solvers boast of "industrial strength" versions handling LP models of up to 2,000 variables, the largest version of What'sBest! has no capacity limit. What'sBest! users routinely solve models of well over 100,000 variables.

**Reliability**

Day in and day out, thousands of companies around the world rely on What'sBest! to provide critical solutions to their toughest optimization problems. What'sBest! is able to solve complex and numerically difficult problems that competing products simply cannot.

**Linear Solvers**

**Primal and Dual Simplex Solvers**

The base version includes the Primal and Dual Simplex solvers, which incorporate numerous enhancements for maximum speed and robustness. Pricing options, for instance, include partial pricing and Devex. The solver dynamically chooses the best pricing option based upon problem characteristics.

**Barrier Solver**

The optional Barrier solver provides an alternative means of solving linear models. The Barrier option utilizes a barrier or interior point method to solve linear models. Unlike the Simplex solvers that move along the exterior of the feasible region, the Barrier solver moves through the interior space to find the optimum. Depending upon the size and structure of a particular model, the Barrier solver may be significantly faster than the Simplex solvers and can provide exceptional speed on large linear models -- particularly on sparse models with more than 5,000 constraints or highly degenerate models.

**Integer Solver**

For models with general and binary integer restrictions, What'sBest! includes an integer solver that works in conjunction with the linear and nonlinear solvers. For linear models, the integer solver does extensive preprocessing and adds constraint "cuts" of several different varieties to greatly improve solution times on large classes of integer models.

**Nonlinear Solvers**

What'sBest! includes a number of ways to find locally or globally optimal solutions to nonlinear models.

**General Nonlinear Solver**

For nonlinear programming models, the primary underlying technique used by What'sBest's optional nonlinear solver is based upon a Generalized Reduction Gradient (GRG) algorithm. However, to help get a good feasible solution quickly, What'sBest! also incorporates Successive Linear Programming (SLP). The nonlinear solver takes advantage of sparsity for improved speed and more efficient memory usage. The Nonlinear license option is required to solve nonlinear models.

**Global Solver**

Local search solvers are generally designed to search only until they have identified a local optimum. If the model is non-convex, other local optima may exist that yield significantly better solutions. Rather than stopping after the first local optimum is found, the global solver will search until the global optimum is confirmed. The global solver converts the original non-convex, nonlinear problem into several convex, linear subproblems. Then, it uses the branch-and-bound technique to exhaustively search over these subproblems for the global solution. The nonlinear and global license options are required to utilize the global optmization capabilities.

**Multistart Solver**

When limited time makes searching for the global optimum prohibitive, the multistart solver can be a powerful tool for finding good solutions more quickly. This intelligently generates a set of candidate starting points in the solution space. Then, the general nonlinear solver intelligently selects a subset of these to initialize a series of local optimizations. For non-convex nonlinear models, the quality of the solution returned by the multistart solver will be superior to that of the general nonlinear solver. The nonlinear and global license options are required to utilize the multistart capabilities.

**Quadratic Solver**

In addition to solving linear models, the barrier option in What'sBest! can automatically detect and solve models in which the objective function includes quadratic terms. By taking advantage of the quadratic structure, What'sBest! can solve these models much more quickly than using the general nonlinear solver. What'sBest! can even handle quadratic models with binary and general integer restrictions. These quadratic capabilities make What'sBest! suitable for applications such as portfolio optimization problems, constrained regression problems, and certain classes of difficult logistics problems (e.g., layout problems, fixed-charge-network problems with quadratic objective). The quadratic solver is included in the Barrier license option.

**Stochastic Programming Solver**

Incorporate risk into multi-stage optimization models, maximize expected profit, and summarize results in histograms showing the distribution of possible profit, etc. This new option allows modeling and optimization for models with uncertain elements via multistage stochastic linear, nonlinear and integer stochastic programming (SP). Benders decomposition is used for solving large linear SP models. Deterministic equivalent method is used for solving nonlinear and integer SP models. Support is available for over 20 distribution types (discrete or continuous). The Stochastic Programming solver is included in the Stochastic Programming option.

**Preprocessing**

Preprocessing routines are included in all solvers. The linear and nonlinear solver include scaling and model reduction techniques. Scaling procedures can improve speed and robustness on numerically difficult models. Model reduction techniques cn often make models solve faster by analyzing the original formulation and mathematically condensing it into a smaller problem. The integer solver includes extensive preprocessing and cut generatin routines.

What'sBest! is designed, so the process of solving the model requires as little input from the user as possible. When the Solve command is initiated, What'sBest! analyzes the problem and, when possible, reduces the problem and even substitutes out variables. Based upon the models structure, What'sBest! automatically selects the appropriate solver and intelligently adjusts internal parameters.

**Linearization**

What'sBest! linearization capabilities can dramatically improve performance on certain nonlinear models. The feature can automatically convert many nonsmooth Excel functions (e.g., IF, MAX, MIN and ABS) as well as the product of a continuous and binary variable into a series of linear, mathematically equivalent expressions. Many nonsmooth models may be entirely linearized. This allows the linear solver to quickly find a global solution to what would have otherwise been an intractable problem.

**Intelligent Integration**

What'sBest! handles the details of the solution process, so you can focus on modeling. When the Solve command is initiated, What'sBest! analyzes the problem and, when possible, reduces the problem and even substitutes out variables. With What'sBest!, you never have to specify whether to use the linear or nonlinear solver. Based upon the model's structure, What'sBest! automatically selects the appropriate solver and intelligently adjusts internal parameters.

Excel users will find What's*Best!* easy to learn and use. What's*Best!* is designed to make optimization modeling a natural extension of Excel. You can quickly build models in a free form manner using standard Excel equations.

**Begin Optimizing in Minutes**

What'sBest! takes full advantage of Excel's flexibility and ease of use. If you are comfortable using Excel, you will probably be able to begin building your first What'sBest! model within minutes of installations. For What'sBest!, all of the optimization information is stored in a natural manner within the worksheet. Constraints and relationships are expressed using standard Excel style functions. What'sBest! models are very visual and interactive -- constraints display their status (violated, satisfied, or precisely satisfied).

**Comprehensive Error Handling**

What'sBest! makes tracking down any problems in your optimization model easy. It provides comprehensive model checking, warnings and error messages. If a problem is encountered during the solution process, What'sBest! provides a detailed description of the problem, and lists cell addresses that are contributing to the problem when appropriate.

**Creating a What'sBest! model is as easy as A-B-C**

**A - Adjustable Cells**

Specify the cells in your Excel workbook that What'sBest! can adjust to find the best solution. In traditional math programming terms, the Adjustable cells are the variables of your optimization problem. Your Adjustable cells may be in one neat cell range or scattered throughout the workbook. You can allow them to take any value or restrict them to whole numbers (i.e., integer values).

**B - Best Cell**

Specify the cell you wish to maximize or minimize. In traditional math programming terms, the Best cell is your objective function. The most common Best cells are to minimize cost, waste, or risk; or to maximize profit, production, or utility.

**C - Constraints**

Specify the restrictions or limitations on the problem. These are the relationships that must be satisfied for the solution to be feasible. Examples of constraints might be the amount produced cannot exceed the production capacity, or the amount shipped to the customer must be equal to the customer's demand. Constraints are expressed using standard Excel style equations, so they are easy to read and understand. What'sBest! constraints display their status (i.e., you can see if they are violated or met).

**Organize your Model on Multiple Sheets**

What'sBest! allows you to build optimization models that take full advantage of the three dimensional modeling capabilities of Excel. The ability to organize information over several tabbed sheets in a single Excel workbook file can be especially useful for large models and models that involve multiple periods or locations.

You can provide easy to use optimization applications in the spreadsheet form for managers and more experienced spreadsheet users or as turn-key applications for less sophisticated users.

**Solutions in a Familiar and Friendly Environment**

What'sBest! allows you to provide solutions in an environment that is entirely comfortable for the average business person. Excel is the most popular modeling tool in use today, and millions of people are at ease navigating their way through spreadsheets full of data and formulas. With What'sBest!, you can build an optimization model in Excel that business people can not only use, but understand. The more the user understands and trusts the application, the more likely it is to be implemented and used effectively.

**Create Custom Applications**

In some instances, you need a more protected environment than an ordinary spreasheet can provide. What'sBest! allows you to easily build full fledged applications that guard against accidentally deleting or overwriting critical data and formulas. It can also allow you to hide your formulation and any proprietary information from the user. What'sBest! includes a full Visual Basic interface that allows you to run What'sBest! commands from an Excel Macro. Using Visual Basic, you can build a sleek, seamless interface to your optimization applications that can include customized input screens and tailored reports.

What'sBest! comes with all of the tools you need to get started quickly and easily.

**The What'sBest! User's Manual**

This 250+ page manual provides complete information on all aspects of utilizing What'sBest! to solve your optimization problems. The manual includes a full tutorial that walks you through building and solving your first model to analyzing the solution. The What'sBest! User's Manual describes all of the commands and features of What'sBest!. Also included is an extensive Sample Models section that illustrates how to use What'sBest! to solve a wide variety of optimization applications.

**Comprehensive Online Help**

What'sBest's extensive Help system lets you conveniently access information on the fly. Not only are the entire contents of the What'sBest! User's Manual available at the click of your mouse, but the Help file also contains up-to-date information on any enhancements added since the documentation went to press.