**HPLX.NET REVIEWS
Derive 4.x for DOS**

Publisher/Manufacturer: Soft Warehouse

Contact: http://www.derive.com

Price: $199.95 upgrade

For most purposes, the built-in software in the 200LX provides great math support. The combination of HP Calc and Lotus 1-2-3 delivers great support for everything from simple arithmetic and solving equations to calculating payroll withholding from tax tables. But sometimes, you need more power than the built-in apps can provide. For that tricky calculus class, or for an engineer in need of some powerful portable assistance, or almost any complicated symbolic math at all, the thing to run on the palmtop is Derive.

Derive is described as a computer algebra system by its publisher, SoftWarehouse. This describes the basic purpose of the application: rather than a calculator or a spreadsheet, it is designed to do algebraic operations on more complex and abstract math problems. The software built into the TI-92 calculator is based on Derive. For HP users, picture a 48GX with Erable, ALG48, and every other package you can get for the 48, with a larger screen and a faster processor.

Derive can handle arithmetic operations, though the interface is somewhat clunky for doing things like 2+2. More complicated operations may benefit from Derive's power, however. For example, Derive can deal with huge numbers much more neatly than a calculator. Derive will even find ratios of numbers to an incredible accuracy-- a hundred-digit number divided by another hundred-digit number. As a simple example, if you approximate SQRT(2)+.02 to 25 digits, it will give you 717106749925661611656259/500000000000000000000000 as a result-- instantly.

Anybody who's taken algebra knows that finding determinants of matrices larger than 2x2 is a pain. Most graphing calculators will allow you to input a numeric matrix and find the determinant automatically. Derive handles this quite well, of course. But in addition, Derive allows you to do operations on symbolic matrices as well. Figure 1 shows a symbolic matrix determinant-- and rather than going through a complicated process of finding 2x2 determinants by hand, you can have it solved in 0.2 seconds on a double-speed palmtop.

Figure 1: Symbolic matrix determinant

For trigonometry, Derive is excellent. Figure 2 [trig.gif] shows some of the trigonometric identities that Derive has built-in, and how it can simplify them symbolically. This particular example solved in 0.5 seconds on my double-speed palmtop.

Figure 2: Trigonometric identities

For calculus, Derive is like walking around with a differential and integral text reference, solving most of the equations in the CRC Handbook tables. For the early calculus subjects-- sums and limits and the like-- Derive can be a great learning tool. Figure 3 shows three three different examples-- a series sum, a product sum, and a limit. Notice that Derive can take limits from either direction-- or both directions. All of the above examples simplify in under two seconds.

Figure 3: Simple calculus functions

Figure 4 shows how Derive can do complex definite integrals-- notice that in this example, one of the limits of integration is infinity. Derive can handle it just fine, and finds the result in a very readable format. The above integral takes only 0.6 seconds to solve on a double-speed palmtop. Without a symbolic math program, this integral would probably have to be looked up in an integral table such as Gradshteyn and Ryshik.

Figure 4: Symbolic definite integral

Figure 5 shows that Derive can also do symbolic indefinite integrals. In order to solve this without Derive you would have to use several rules of integration-- slow and inaccurate. Or plug it into the palmtop and get a solution in 3.5 seconds.

Figure 5: Symbolic indefinite integral

Derive can also do fantastic plots, both 2D and 3D. Figure 6 shows a 2D implicit circle plot on the 200LX (x^2+y^2=16). For 3D plotting, figure 7 shows what the 200LX can do. Figure 8 is an impressive shows what can be done on a VGA monitor. On the palmtop, despite the more modest graphics capabilities, 3D plots can still be drawn. They just take more time.

Figure 6: Two-dimensional plot in "split-screen" mode, on 200LX

Figure 7: Two-dimensional plot [x^2+y^2=16] and three-dimensional plots [for z=SQRT(16-x^2-y^2)] on 200LX

Figure 8: Derive 4.0 for Windows plot

One nice feature of Derive is that it isn't limited to built-in functions. You can define custom formulas and functions, somewhat like the HP Solver application. This allows expansion of the base capabilities of Derive so you can do even more powerful calculations. For example, figure 9 shows a second-order differential equation that was solved by functions in the ODE.MTH file.

Figure 9: Second-order differential equation handled by ODE.MTH

Derive will also do unit calculations, and can handle your own custom-defined units. If you have a need to convert kilometers per hour to apples per orange, you can define such a conversion in Derive without a problem.

Derive can be run in either graphics or text mode, depending on your preference. Text mode is faster, especially when plotting, but obviously is far less accurate.

Derive can also export expressions to programming languages-- BASIC, Pascal, C, and Fortran. You can use Derive to build complicated expressions and then import them, ready-made, into your programs.

The latest version of Derive, 4.x (4.13 as of this writing), runs quite well on the palmtop. The new version offers several new functions over the previous version, as well as one main feature: it can be used on a 200LX or another real-mode machine just fine, but will automatically take advantage of extended memory on more powerful desktops. This eliminates the need for the two separate executables that the previous versions used. Speedwise, the new version seems about on par with the 3.x versions. For a complete list of new features, see http://www.derive.com/dfd4feat.htm.

In conclusion, if your math needs exceed the built-in capabilities of the 200LX, buy Derive. You won't be sorry.

Copyright 1999, David Sargeant.

Last Updated 1-2-1999

*Webmaster*