TK Solver was one of the first general-purpose problem solvers for desktop PCs, originally released in 1982 and dubbed as an equation solver. Since then, the product has steadily matured. Reviews in the mid- to late-1980s applauded its unique iterative solving and backsolving powers but consistently criticized its multi-sheet, multi-level text-based interface as being too confusing for occasional users. Since the interface was completely overhauled in the 1990s to run on the Windows platform, navigation and use of the program have been simplified. They are much more intuitive, and once the user becomes familiar with the program's structure and tools, its well-organized system for model-building and problem-solving is not difficult to use.

The current version, TK Solver 5.0, strives also to be a useful tool for application developers through links with Excel, browsers, Microsoft Visual Basic, .NET and other popular programming environments. It's a simple task, for example, to incorporate the variables from several TK Solver models within a single, dynamic Excel application. Clearly, today's TK Solver is much more than an equation solver.

New Features in TK Solver 5.0


Some of the new features in TK Solver 5.0 that may be of interest to O.R. professionals and/or students are:

• Easy-to-use optimization wizard for linear, nonlinear, binary and integer problems. The algorithms used are licensed from Frontline Systems, makers of the popular Excel Solver. The version included with TK Solver is more current than the Excel add-in and can deal with larger problems.
  
  
• Expanded collection of numerical solvers for differential equations.
  
  
• List fills that now include random number generation for simulations.
  
  
• Parameter estimation for a variety of distribution functions.
  
  
• Dynamic Excel Link that allows multiple TK Solver models to interact with Excel.
  
  
• TK Solver/Excel applications that can be bundled for distribution to non-TK Solver users.
  
  
• A RuleMaster option that allows TK Solver applications to be distributed over the Internet.
  
  
• A Report Writer that displays all aspects of the math model in a customizable configuration, including formatted equations in the sequence they are solved.
  
  
• Plotting now includes programmable annotations so that the text and location dynamically update when the model is solved.
  
  
• Startup and Terminate Functions that allow application builders to break up the processing of a model into three stages — data gathering, solving and summary.
  
  
• Built-in functions that can be accessed through Function Wizards, providing step-by-step guidance in their syntax and use.
  
  
• Forty new functions for matrix processing.

TK Solver takes a completely different approach, making the assumption that the model builder will often desire to reuse it to solve related problems that may not follow the original sequence of steps. With this in mind, all the variables are summarized on a single work sheet. Variables can interchangeably be defined as inputs or outputs. The same concept applies for other types of objects in the model. There are separate sheets for storing functions, lists, tables, plots, unit conversions, numeric formats and hyperlinked comments. All these sheets are accessible in a variety of ways, with the most prominent being a Navigation Bar on the left edge of the screen.

The program includes Wizards for all sorts of activities, from using built-in functions to generating tables of plots, to importing unit conversion factors. The unit conversion library is extensive, and engineers should be able to find what they need there. If not, it is simple to add whatever additional conversions are required.

I can see how reviewers 20 years ago may have gotten confused by having to memorize a series of keystrokes to find their way in and around all of these sheets. But Windows has been kind to TK Solver — the interface is easy to work with.

TK Solver's Rule-Based Language


If you have never used a rule-based language like that in TK Solver, you're in for a real treat. Entering equations couldn't be easier. You simply enter them just as you know them, without worrying about the sequence or the location of the unknowns. For example, Figure 1 shows some of the equations for a single-server, unlimited queue problem, as entered in TK Solver.

Figure 1

As the equations are entered on a single line — like you would in Visual basic or C — they're instantly displayed in MathLook view on the screen as well as in the reports. That helps you immediately check if you entered the equation correctly. A Greek palette is also available for entering those characters.

A Variables Window displays all the variables in the model, and this is where you supply input values, units and descriptions. Figure 2 displays the Variables Window for this example with sample inputs provided along with the results after solving.

Figure 2

The same model can solve many different problems. Suppose you want to reduce the expected waiting time in the system (W) from 18 minutes to just five minutes. What must the new service time (st) be? With TK Solver, it's as simple as blanking the value of st, changing W to an input of 5, and solving (Figure 3).

Figure 3

It really is that easy. This is completely different from how such problems must be solved with procedural languages, spreadsheets and math packages. Such alternatives require you to invoke a special solver or optimizer, adding to the complexity and difficulty in application development.

TK Solver's Procedure Language


Since mathematical models require more than just systems of equations, TK Solver allows you to create procedure functions for incorporating such things as for-next loops, recursion, go-to's, and other constructs. These functions then act as subroutines within the overall rule-based environment, meaning that even procedure functions can be backsolved if necessary. Figure 4 gives a sample procedure function to generate lists of probabilities.

Figure 4

There is a lot more to this program than initially meets the eye. There are Flash Tutorials to introduce you to the interface and features. The Help Utility is easy to access and use, too. For example, I found that all the Procedure Language constructs were concisely summarized with examples, and I was able to find this information within a couple of clicks from the function I was building. Browsing the Help Utility is one way to learn more about the software's potential.

One can also learn a lot by visiting the TK Solver Library Menu. This Library contains a collection of tools and examples written in TK Solver. For example, there are functions for finding roots of polynomials, sorting lists or interpolating within tables. There is also an extensive set of routines covering probability and statistics. It really helps to be able to see and understand how these functions were written. This is also the case for the numerous examples in the TK Solver Library. The examples for curve-fitting, optimization and integration of differential equations are vital for understanding these features. Faculty members in particular will find this facility quite helpful in their teaching.

The UTS Web site also includes case studies for some of the more complex modeling issues. There are two case studies on differential equations. I would like to see more of these specifically targeting O.R. topics.

TK Solver 5.0 Premium


UTS offers TK Solver in several "flavors" depending on your budget and power requirements. TK Solver 5.0 Premium is their top-of-the-line offering and adds two key features — Solution Optimizer and TK Solver—Excel Link Packager for Distribution — to the base package.

Solution Optimizer. The Solution Optimizer is essentially a shell around the TK Solver rule-based language. Once a mathematical model is created, you can invoke the Solution Optimizer to solve it within whatever constraints you have. Those familiar with the Excel Solver will feel at home with the Solution Optimizer, as UTS licensed the technology from Frontline Systems, the developers of the Excel Solver. One important difference with this implementation is that TK Solver handles the iterative solution of simultaneous equations on its own, freeing up the Solution Optimizer to independently focus on other, more complex optimization issues.

As mentioned earlier, the TK Solver Library includes a collection of examples to get you familiar with the potential of the Solution Optimizer. Several of them are classic O.R. problems including sales force allocation, facility location, inventory costs, gas blending and portfolio optimization.

There are two options for setting up your Solution Optimizer constraints. UTS decided to include one interface that looks very similar to that of the Excel Solver for those already familiar with it. The other is a more elaborate, step-by-step wizard that walks you through the entire process.

Decision variables can be declared as continuous, integer or binary integer. The program differentiates between "bounds" and "constraints" in the solving process. Bounds are limits beyond which the Solution Optimizer should not attempt to search while constraints can be violated during the optimization process. For example, a global bound can be set that specifies that no decision variables can be negative. Both the constraints and bounds can be set and dynamically updated based on values of other variables in the model.

Figures 5, 6 and 7 are the Optimization Wizard forms.

Figure 5

Figure 6

Figure 7

TK Solver—Excel Link Packager for Distribution. The Packager makes TK Solver attractive for application developers or anyone who wants to share a math model with others. It lets you dynamically link any number of TK Solver models to your Excel spreadsheet to act as subroutines within it. Furthermore, the Packager lets you bundle the models with the spreadsheet and send the file to another Excel user. The recipient does not need to have TK Solver installed to "run" your spreadsheet. A free utility — TK Solver Player for Excel — can be downloaded from the UTS Web site similar to the way Adobe distributes their player for reading PDF files. However, the Player runs entirely behind the scenes once it is downloaded. It was a two-minute job to link my queuing model to Excel and package it. This is a nice feature.

TK Solver and Visual Basic (VBA)


Although many advanced Excel users are probably familiar with using VBA to write subroutines for Excel, I think they would find TK Solver a very useful addition. TK Solver is better at handling the serious number crunching and heavy lifting while VBA can be used to automate various tasks that enhance the interface and overall end-user experience. The combination seems quite powerful.

Queuing Analyses on TK (QTK) Application


QTK is an optional package available from UTS. (A bundled package consisting of TK Solver 5.0 Premium and QTK is priced at $899 with academic pricing also available.) Following is a listing of the modules included in QTK.

Basics


Poisson Probabilities
Mixed Exponential Probabilities
Erlang Probabilities
Finite Markov Chains
Finite Steady-State Birth/Death Solution
Infinite Steady-State Birth/Death Solution
Sample Path for Constant Single-Server Queue
Unit Conversions

Single-Server Queues


M/M/1/K Queue
Markov Single-Server Finite-Source Queue
Simple State-Dependent Service
General Markovian State-Dependent Queue
Impatient Customers: Balking
M/D/1: Deterministic-Service Queue
M/E(k)/1: Erlang Service Queue
E(k)/M/1: Erlang Arrival Queue
M/G/1: Non-Exponential Service
M/G/1: Sensitivity Analysis
D/M/1: Constant Input, Exponential Server
H/M/1: Hyperexponential Interarrivals
G/M/1: Non-Exponential Interarrivals
G/E(k)/1: Non-Exponential Interarrivals
E(j)/E(k)/1: Single-Server Erlang Queue

Multiple-Server Queues


Limited M/M/c/K Queue
Multi-Server Finite-Source Queue
Pure Overflow M/G/c/c
Optimal c for M/G/c/c
Ample Service M/G/infinity
M/E(k)/c: Erlang Service Times
E(k)/M/c: Erlang Interarrival Times
D/M/c: Constant Interarrival Times
H/M/c: Hyperexponential Interarrival Times
G/G/c: Upper and Lower Bounds

Bulk Queues


Fixed Bulk-Input M^[K]/M/1 Queue
Multi-Server Bulk-Input M^[X]/M/c
Bulk Service M/M^[K]/1 Queue (1)
Bulk Service M/M^[K]/1 Queue (2)
Batch Arrival G^[K]/M/1 Queue

Priorities


Markov Priority Queue w/Two Service Rates
M/M/c with Two Priorities, Nonpreemptive
Multi-Priority M/M/1 with One Service Rate
Multi-Priority M/M/1 with Many Service Rates
Multi-Priority M/M/c, Nonpreemptive
Two-Priority Markovian Queue with Preemption
N-Priority Markovian Queue with Preemption
Multi-Priority, Nonpreemptive M/G/1 Queue

Networks


N M/M/1 Queues in a Tree
N M/M/c Queues in a Tree
Closed Jackson Network
Open Jackson Network, 1 server
Open Jackson Network, c Servers

These models come with a 250+-page manual with commentary from Gross and Harris plus sample problems. Unfortunately, while the TK Solver interface has dramatically improved with its adaptation to Windows, the Gross and Harris manual is a relic of the DOS world. While the outdated manual does not prevent using the QTK package or limit its usefulness, it is disappointing to find it included in a premium software package.

The models are easily loaded in to TK Solver, and from there it's just a matter of entering your inputs. Of course, these models can also be linked with Excel spreadsheets and used as subroutines with more elaborate applications.

Documentation


While I was not necessarily pleased with the disconnect between the QTK package manual and the current TK Solver software, I was impressed by the overall documentation for TK Solver. In addition to the Flash Tutorials and Help Utility mentioned earlier, TK Solver also includes one of the most welcome of features — printed manuals. A basic "Getting Started" manual concisely introduces the user to the functions of TK Solver, while a much more extensive User's Guide provides a wealth of more detailed information, giving the user a comprehensive explanation of the available tools and how to use them. In spite of my complaint about the QTK manual, it does offer excellent explanations of the Queuing models and how to use them, and is a valuable component of the package.

MathLook for Excel


MathLook for Excel — based on the same MathLook technology that is built into TK Solver — is an optional add-in for Excel. It does not require you to have TK Solver. It converts Excel formulas into mathematical notation, just like that created by the Instant MathLook feature in TK Solver. However the Excel add-in has additional features.

You can highlight one or more Excel cells, click the MathLook icon, and all your formulas appear in 2D format. One particularly useful feature is formula expansion for cell dependencies. It's possible to create some rather impressive looking equations. All in all, pretty handy if you ever need to audit or document formulas. The tool also includes a grid for naming cells. Anyone working with a lot of Excel formulas shouldn't be without this low-cost utility.

Tolerance Analysis and Monte Carlo Simulation


Product design engineers and industrial engineers may find the UTS application called StackSoft of interest. In any product assembly, individual parts have specific dimensions, which have a certain amount of variability and uncertainty. StackSoft helps the design engineers enter the tolerances for each dimension such that the overall effect on the assembly of parts can be evaluated to make sure that the components will assemble properly. Ideally engineers would want to loosen the tolerances on parts that cost the most, so that their cost can be reduced. The tradeoff might involve tightening the tolerances on relatively inexpensive parts. When properly used, such tradeoff analysis can mean huge cost savings in product manufacturing.

The Monte Carlo simulation feature in StackSoft makes it possible to assign different distributions to the tolerances of various part dimensions in an assembly to assess the overall effect on various production quantities. A classic example might be the valve train assembly in an engine, which involves two dimensional tolerance analysis involving both linear and angular dimensions. With the kind of precision today's engines demand, the tolerance analysis can play a critical part in the design and manufacturing of valve train components.

StackSoft is very easy to use and has its own interface overlaid on TK Solver, so that knowledge of TK Solver is not needed. No extensive knowledge of statistics is required, either. With minimal training and some guidance, designers can create models of tolerance stacks for most assemblies.

I was also fortunate enough to have the privilege of testing UTS's Simulation Wizard. The Simulation Wizard is another TK Solver application that permits the creation of Monte Carlo simulations involving combinations of variables that are more complicated than the simple addition/subtraction available in StackSoft. I found the Simulation Wizard to be the perfect tool for analyzing the relationship between the orientation of machined surfaces and bearing clearances on a shaft assembly — something that StackSoft could not do. While the Simulation Wizard is not commercially available, if UTS can be convinced to offer it, it would be another extremely powerful tool to add to the TK Solver libraries.

Product Information and System Requirements TK Solver 5.0, MathLook for Excel, Queuing Analyses on TK, and StackSoft are available from: Universal Technical Systems, Inc. 200 W. State St., Suite 700 Rockford, IL 61101 Phone: 815-963-2220 Fax: 815-963-8884 E-mail: sales@uts.com URL: www.UTS.com Minimum Requirements for TK Solver 5.0 Microsoft Windows 2000/XP CD—ROM Drive 128 MB RAM 120 MB Hard Disk space 800 x 600 Monitor Resolution MathLook for Excel Add-in Supports: Microsoft Windows 98 and higher Excel 97 and higher Pricing Information: TK Solver 5.0 Premium Edition One-time License Purchase Price Stand Alone — $599 Single Network User — $899        Subscription License Price 25 user subscription $1,500 first year, $1,000 each following year TK Solver 5.0 Standard Edition One-time License Purchase Price Stand Alone — $399 Single Network User — $699 50 user subscription $2,500 first year, $1,750 each following year Queuing Analyses (Requires TK Solver) Contact UTS for bundled pricing options! StackSoft Annual Subscription License Price Stand Alone — $699 Single Network User — $1,199 MathLook for ExcelTM One-time License Purchase Price Stand Alone — $99 Network — $199 per user Contact sales@uts.com for Academic and Site License pricing information.

Vendor Comments Editor's note: It is the policy of OR/MS Today to allow developers of reviewed software an opportunity to clarify and/or comment on the review article. Following are comments by S. M. Marathe, president and CEO of Universal Technical Systems, Inc. TK SolverTM is the industry's longest-standing mathematical modeling software and the calculation engine that powers a number of UTS applications including an expert system for gear design and manufacturing and Interactive Roark's Formulas for computerized structural analysis. In our 20-year history, UTS has heavily invested in R & D to enhance our core TK Solver product. We intend to continue our commitment to developing industry-standard technology that empowers engineers and other professionals in their everyday work. We are always looking for ways to improve our products and would welcome the opportunity to partner with and would invite O.R. subject matter experts to contact us with suggestions and new product ideas. • Product documentation for Queuing Analyses: Guilty as charged! The user manual was indeed a "relic" and has since been completely updated. It is now on par with the TK Solver documentation. • Queuing Analyses an instructional tool and easy enhancement platform: The open and declarative nature of TK Solver makes it a natural tool for teaching because you can see exactly how the models are built. TK Solver models are very compact, and that makes modifying or enhancing them especially convenient because it can be done all in one place. Students and OR/MS professionals alike will find QTK much easier to use than traditional procedural language programming. • New TK Solver 5.0 Premium features: We've gotten some great feedback from customers on our brand new Packager and Player technology. The Packager component allows users to dynamically link a number of TK Solver models to an Excel spreadsheet and essentially "package" the files for distribution. The Player component is a free download from the UTS Web site that allows any Excel user to interact with the model by changing inputs and instantly viewing outputs. It also leverages a wealth of TK Solver functionality—all in a familiar Excel interface. • Simulation Wizard for "Monte Carlo" simulations: While we have yet to make a final decision regarding the release of this product, we truly appreciate the reviewer's vote of confidence! We would be willing to have a select group of OR/MS Today readers "preview" the technology for further evaluation. Interested parties should contact sales@uts.com.

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