The expression entry is the most important part of the Qalculate! user interface. The normal calculation procedure in Qalculate! is to type in a mathematical expression (ex. ?5+5?) and press Enter (or click Execute). The result (?10?) is then displayed below the expression entry in the result display.

Figure 2.2. Completion

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Qalculate! helps out with the expression by giving a list of possible endings to words representing functions, variables and units. The list will narrow with each letter typed. Select an item in the list and the name will be completed. If a function was selected, parenthesis will be added and the position moved for immediate entry of arguments.

As the expression is typed in, the area directly direclty below the expression entry, to the left, will show useful information. By default the calculator's interpretation of the expression is shown (ex. ?5 * meter? for ?5m?). The interpretation will be displayed in red (configurable) if there are errors in the expression or in blue for lesser errors (for example too many arguments in a function). If the last typed in text represents a function, and arguments are about to be entered, the functions name and its arguments will be displayed. The first argument in the information text is highlighted and includes information about its type and restrictions and when an argument has been entered, the next will be highlighted.

After execution of an expression, the whole expression will be marked. This normally means that if something new is entered, the old expression will be overwritten. If, however, an operator (+, ?, *, /, ^) is entered first, the old expression will instead be the target of action. The operator will then apply to the whole expression, which is put in parenthesis. This works on all marked ranges, meaning that this way an expression can conveniently be put in parenthesis. Functions set the selection as their first argument.

The Up and Down keys will access previously entered expressions. With focus in the expression entry, Up traverses backwards in the expression history and Down forward.

The font used for the expression entry can be selected in the preferences dialog (Edit ? Configure Qalculate!).

The result of calculations is displayed in the open area below the expression entry. The font used for the result display can be selected in the preferences dialog (Edit ? Configure Qalculate!). Use of Unicode signs can be turned off in the same dialog. Otherwise Qalculate! will try to make the result as fancy as possible and print ? for pi, ? for sqrt, ? for euro, and so on. Information about customization of the mathematical result output is available in Chapter 4, Calculator Modes.

In front of the result an equals or approximately equals sign is shown. This indicates whether Qalculate! was able to calculate/display the result exact or only approximate, in the current mode.

The result display has a context menu, which pops up when clicking with the right mouse button anywhere in the field. This menu provides a subset of the display alternatives from the mode menu (Table 2.4, ?Mode Menu?) and some actions from the edit menu (Table 2.3, ?Edit Menu?). See more info in Chapter 4, Calculator Modes. Show Parsed Expression shows how the entered expression was interpreted before the calculation leading to the current result.

When you move the mouse over parts of the result, descriptions will pop up for variables, functions and units. This will only work if you have tooltips enabled in KDE. You can also show this information by double clicking or selecting Show Object Info in the context menu. For matrices and vectors, this will open a window with a spreadsheet-like table displaying the contents of the matrix/vector.

To copy the result, either select Edit ? Copy Result, or mark and copy the text from the result display or history. Note that all results are not displayed in the result display as an expression which can be used directly in the expression entry. This is true for divisions, powers and vectors. For example, when the result "x^5" is marked and copied, the power sign will be lost.

The keypad provides access to a fairly small set of traditional calculator buttons, which work as expected. The top buttons (from left to right) toggles exact calculation, toggles fractional number display, selects display mode and selects number base in result (see Chapter 4, Calculator Modes).

Figure 2.3. Keypad

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The history view provides access to previous calculation results (50 rows are reloaded on restart). Previous expressions and results, as well as errors and warnings, are displayed in plain text and can be marked and copied (from the right-button context menu or with Ctrl+C) to the expression entry or elsewhere.

Figure 2.4. Calculation History

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The menus in the menu bar provides access to most of the functionality of Qalculate!. Their contents are listed and described below.

The manager windows provide a structural way of working with variables, functions and units (collectively referred to as objects). The managers for the three different objects are essentially similar. They can be opened from the edit menu. F2, F3 and F4 can also be used for variables, functions and units respectively. The function manager can also be opened with the f(x) button in the keypad.

Figure 2.5. Variable Manager

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To the left is a category tree and beside that is a list of all objects in the selected category, including all subcategories. Objects without a category are put under ?Uncategorized?. The top category, ?All?, provides a list of all objects, except those that are deactivated and available in the second top-level category ? ?Inactive?. The object list does, in addition to descriptive names, for variables have an extra column for values of variables, and units have additional columns for abbreviation/singular/plural and base unit.

The buttons on the right work on the selected object in the list. New opens a dialog for creation of a new object, while Edit opens the same dialog to edit the selected unit. Insert inserts the object into the expression entry in the main window, Delete removes the object and (De)activate toggles recognition in expressions on/off. The unit manager has an additional button for conversion of the current result and the variable manager a button for export to a data file.

Figure 2.6. Function Manager

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The function manager has a description box at the bottom, which shows the syntax, description and arguments of the selected function.

Figure 2.7. Unit Manager

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The unit manager has an area for quick conversion between units. This converts between the selected unit in the list and the selected unit in the option menu. The menu contains the same units that are available in the list. Units are converted by specification of a quantity, in the entry next to the unit to convert from, followed by Enter.

For more information about variables, functions and units, see Chapter 5, Variables, Chapter 6, Functions and Chapter 7, Units.

The number bases dialog, accessible from the File Menu, is an efficient and convenient tool for conversion between binary, octal, decimal and hexadecimal numbers. This dialog contains entries for each number base. When a number is typed in any of the entries, the others are automatically updated to display the current number in their format. Numbers, or expressions, entered follow the same rules as expressions in the main expression entry.

Figure 2.8. Convert Number Bases Dialog

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The following operators are defined in Qalculate! and may be used in expressions.

The operator names ?plus?, ?minus?, ?times?, ?per?, ?AND? and ?OR? may also be used, surrounded by space, for the corresponding operation (ex. ?5 plus 2?, but not ?5plus2?, equals ?5 + 2?). These operator names are localized, but ?AND? and ?OR? are always available. In addition to these operators there are a couple of shortcuts for certain functions, such as ?5!? which equals ?factorial(5)?.

The multiplication sign can generally be left out. This is not true for numbers (?5(5) = 25? but ?5 5 = 55?). Expressions can also generally be written with or without spaces with the same result (?2xsin(2)? equals ?2 x sin(2)? which equals ?2*x*sin(2)?), but be careful. The vast number of functions and units means that without separating spaces, the result might not be obvious. To avoid confusion Qalculate! can limit the use of implicit multiplication (Mode ? Limit Implicit Multiplication), so that space, operator or parenthesis must be put between functions, units and variables (in this mode ?esqrt(5)? does not equal ?e * sqrt(5)?). Also note that unit prefixes must be put immediately before the unit, to be interpreted as prefixes (?5 mm = 0.005 m?, but ?5 m m = 5m^2?). You can see how to expression was interpreted in the history window.

Usually, mathematical expressions are written as normally expected. Standard operator precedence apply. Expressions are evaluated according to the following priorities:

Vectors and matrices are most effectively used stored in a variable. Qalculate! provides separate tools for these variables. They use a different dialog, where each element can be edited separately as in a spreadsheet. As with other variables, click Edit in the variable manager to edit a matrix/vector variable, but to create a new, select File ? New ? Matrix or File ? New ? Vector.

Figure 5.3. Matrix/Vector Edit Dialog

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In this dialog, name, category and descriptive name are typed in as usual, but instead of a single value entry, the matrix/vector edit dialog has a table of entries. Select number of rows and columns above. In a vector this only determines how many value entries that are shown in the table and empty entries will be ignored. For matrices, each entry in the table is an element in the matrix. It is possible to switch between matrix and vector in the dialog (the menu item selected only determines the initial mode).

Matrices and vectors can also be loaded from data files. These files most be plain text files with values organized in separated rows and columns. Select File ? Import CSV File... and a dialog window pops up. First select the file to import and then specify whether if it shall be imported as a matrix or vectors. A name, descriptive name and category can optionally be typed in. If the name field is empty, the file name will be used instead. After that, the row in the file where the data starts should be specified. as well as whether this first row contains column headings. Finally the delimiter, used to separate columns in the file, must be selected. Click OK and variables will be generated from the file. If vectors are to be generated and the file contains more than one column, the name will be used as a subcategory and each variable will add the column heading (or ?Column 1?, ?Column 2?, ...) to the name and the descriptive name.

Figure 5.4. Import CSV Dialog

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The load() function can be used to access a CSV file directly in an expression. The reversed action is also available with export(), or the dialog accessed with File ? Export CSV File... or from the variable manager.

Functions are a bit more complex than variables, but can nevertheless be relatively easily created. File ? New ? Function or click New in the function manager and the function edit dialog pops up. This dialog consists of two tabs/pages; the first with general descriptive information and the last for the function definition. First enter a name, used to reference the function in an expression. If an expression is entered a bit further down, then the function will already be fully working. A bit more does however need to be said about the function expression.

The expression of a function is basically a normal expression with placeholders for arguments. These placeholders consists of a backslash and a letter ? x, y, z for the 1st, 2nd and 3rd arguments and a to u for argument 4 to 24. They are replaced by entered arguments when a function is calculated. The placeholders naturally also decide the number of arguments that a function requires. For example the function for triangle area (?base * height / 2?) has the name triangle and the expression ?(\x*\y)/2?, which gives that ?triangle(2, 3)? equals ?(2*3) / 2? and returns ?3? as result. An argument can be used more than one time and all arguments must not necessarily be in order in the expression.

Figure 6.2. Function Edit Dialog

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Additionally, optional arguments can be put in the expression with upper-case (X, Y, Z, ...) instead of lower-case letters (x, y, z, ...). The default value can be put in brackets after the letter (ex. ?\X{2}?). The default value may be omitted and is then zero. All additional arguments after an optional argument must also be optional.

A condition that must be true (>0) for the function to be calculated, can optionally be entered in the text field below the expression. This follows the same conventions as function expressions. For example if the second argument must be higher than the first, ?\y > \x? may be entered as condition.

Further, name, type and condition for each argument can be specified.

To keep functions well organized, supply a category, descriptive name and description. A function can also hidden from menus with the corresponding check box, which can be useful for sub functions.

Global, system-wide functions can not actually be changed by the user, but if one of these functions is edited, they are deactivated and seemingly replaced by a new function. This way global functions can be ?deleted? by deactivation. Some functions are however hard-coded and cannot be changed by the user.

Expressions can be converted to a specific unit directly in the expression entry with the ?to? operator, which converts the left-hand expression to a specified unit (ex. ?5 feet + 2 inches to cm? converts the result of ?5 feet + 2 inches? to centimeters and displays it). Unit expressions may only contain units, prefixes, exponents, multiplication and division. Other elements are ignored.

The unit conversion dialog, accessible from the Convert button, Edit ? Convert To Unit Expression... or Ctrl+T, can also be used. Enter a unit in the dialog that pops up, click Apply or OK and the displayed result is then converted. In this dialog, you can also select a unit from a list accessed by clicking Selector >>. When a unit is selected from the list the expression is updated and Apply automatically pressed.

Figure 7.1. Unit Conversion Dialog

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The final way to convert to another unit is to use the predefined units in the Edit ? Convert To Unit menu or press Convert Result in the unit manager. Edit ? Set Prefix can be used to select a prefix.

It is also possible to let Qalculate! automagically convert the result to appropriate units with Edit ? Convert To Best Unit or Edit ? Convert To Base Units. If instead the corresponding choice is selected from Mode+Unit Display, each result will automatically be converted until the choice is deactivated (Mode+Unit Display ? No Automatic Conversion).

There are three different unit classes in Qalculate! ? base, alias and composite units. Base units are units defined as basis for other units. Meters and seconds are typical base units. Alias units is defined in relation to another unit. For example, hour is defined as an alias unit that equals 60 minutes which in turn is defined in relation to seconds. Finally, composite units are defined by a unit expression with multiple units. Composite units often have an alias unit associated with them, as they do not have a reference name on their own. For example, a joule is defined as an alias defined in relation to a composite unit defined as ?Newton * meter?.

Select File ? New ? Unit, or click New in the unit manager, and the unit edit dialog pops up.

Figure 7.2. Unit Edit Dialog

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First the unit class needs to be selected. Depending on the unit class, different elements in the dialog will be enabled. For all units, category and descriptive name can be specified to keep them well organized. A unit can also be hidden from unit menus with the corresponding check box, which can be useful for some composite units.

Base and alias units normally have three different name forms defined for use in expressions ? abbreviation (ex. ?m?), singular (?meter?) and plural (?meters?). Composite units only have an internal name, used to reference the unit in definitions of other units.

For base units, the name is all that is needed. For alias units, on the other hand, a base unit, exponent and relation are necessary. For more complex relations an inverse relation can also be specified for conversion back from the base unit. The base unit must not necessarily be of the base unit class and it is recommended that an alias unit is defined in relation to the closest unit (ex. 1ft = 3 hands, 1 hand = 4 in, and 1 in = 0.0254 m). The relation is usually just a number that tells how large quantity of the base unit is needed to get the alias unit (alias unit = base unit * relation). More complex units can specify the relation as a full-blown expression where ?\x? is replaced by the quantity of the base unit and ?\y? is the exponent. For example, Degrees Celsius has the relation ?\x + 273.15? and the inverse relation ?\x ? 273.15? to the base unit Kelvin. For simple relations, the reversion is automatic and ought not be defined separately. The check box below relation in the dialog specifies if the relation is exact or approximate. The exponent defines the exponential relation to the base unit, so that the alias unit equals the base unit raised to the exponent. For simple unit relations this gives: alias unit = relation * base unit^exponent.

Composite units need a unit expression with multiple units as base, in the base unit field. These expressions may only contain units, prefixes, exponents, multiplication and division (ex. ?km/h?).