The Slide Rule

Nov 22 2008 News:
Minor update to Slide Rule for Maemo released. I have changed the keypad to look more like calculator instead of the phone dialpad. Also, the top row of N810 keys can now be used as digits without pressing the F-key.

What is it?

At the surface, the Slide Rule is just another calculator for your mobile phone. In addition to the usual arithmetic duties, Slide Rule can do much more though:

• Simplify ratios without resorting to floating point.
• Simplify algebraic expressions.
• Plot algebraic expressions.
• Compute derivatives analytically.

The latest version of the Slide Rule can always be obtained from the home page. To get help, report bugs, suggest new features, and discuss Slide Rule and my other applications, use the discussion group at Google Groups. Now, let us look closely at how you install and use the Slide Rule.

Downloads

Installation

The Slide Rule will run on any Nokia phone equipped with the 3rd Edition of the S60 software. It will not run on older S60 phones or UIQ phones from Sony Ericsson.

To install Slide Rule, download its .SIS file to your phone and open it. If installation fails, you may have to enable the phone to install applications from providers other than Nokia affiliates. To do this, go to Tools | Application Manager | Options | Settings and set "Software Installation" setting to "All".

Basic Operations

When you open Slide Rule application, it presents you with a screen shown above. The green area at the top displays the most recent computation results. It is similar to a paper roll in a printing calculator. The yellow area at the bottom serves to enter data. Just like in a traditional calculator, you type in arithmetic or algebraic expressions and get the answer by pressing the central button on the directional pad. If your phone is blessed with a QWERTY keyboard, it will work in the expected way. To enter data with the dialpad, use it as follows:

• The red [END] button quits the application.
• If your phone is blessed with a QWERTY keyboard, it will work in the expected way.
• Dialpad digits [0]..[9] act (surprise!) as digits.
• [LEFT], [RIGHT], [UP], and [DOWN] on the directional pad correspond to arithmetic operations "-", "+", "*", and "/", similar to many other calculator applications.
• [#] enters the decimal point (".").
• [*] enters the variable name "x".
• [&larr], [C] delete entered characters. If there are no characters, these keys will delete the most recent result off the list.
• [ENTER] key or the [OK] button on the directional pad enter your new expression into the calculator.
• [SOFT1] switches between calculator and plotter modes.
• [SOFT2] opens a menu of often used functions (sine, cosine, logarithm, etc.). Pressing [OK] inside this menu enters the equal sign ("=") and computes the numeric value of the most recent result.
• The green [SEND] button opens a menu of rarely used functions (arcsine, arccosine, hyperbolic functions, etc.).

• Any complete expression (like 34.5*12+3.9, sin(1.5)*cos(0.7) or sqrt(25)/9^3) is computed and its result put on the list.
• Any complete expression with variables gets simplified as much as possible and then put on the list.
• An incomplete expression starting with "-", "+", "*", "/", or "^" (such as +12, ^2+0.3, or /exp(10)) gets concatenated to the end of the last expression and then computed.
• An incomplete expression ending with "-", "+", "*", "/", or "^" (such as 12+, 0.3+2^, or exp(10)/) gets concatenated to the beginning of the last expression and then computed.
• If you put a function name without any arguments (like log or sqr), the program will use the last expression on the list as the argument.
• If you put a "-", "+", "*", "/", or "^" sign without any arguments, the program will operate on the last two expressions from the list.
• If you enter d<variable> (i.e. dx, dy, dt, etc.), the program will compute the corresponding derivative of the last expression and save result back to the list.

Arithmetic Operations

Upon clicking the [OK] button, the Slide Rule will try to evaluate any expression you enter numerically. This is possible when your expression does not contain any variables or all the variables can be reduced out of it. So, expressions like "1+13", "0.75/36+19", or "sin(0)*sqrt(x)" will result in immediate numeric answers. Any expression that cannot be evaluated to a numeric value, will only be simplified and treated as a function.

Unlike a traditional calculator, the Slide Rule attempts to keep integer and floating point portions of the answer separate, to avoid losing precision. While the floating point portions are treated in the usual manner, there are special rules when dealing with integers:

• Integer addition, multiplication, and subtration happen normally, unless the result becomes too big. In this case, it is converted to a floating point value.
• Integer division creates a ratio. The Slide Rule will simplify this ratio as far as it can (i.e. 22/143 becomes 2/13 and so forth), but will not convert it to floating point.

Algebraic Operations

Plotting Graphs

When in the calculator mode, you will see that some expressions are marked with colored letters  G . Press [SOFT1] to see graphs of these expressions in corresponding colors. While in the plotter mode, shown at the right, you can use the following keys:

• [SOFT1] returns back to the calculator mode.
• [SOFT2] zooms out the graphs.
• [OK] button on the directional pad zooms in.
• Directional pad buttons move the coordinate plane.
• [#] adjusts vertical scale to bring graphs into focus.
• [*] resets scale and position.