# Expressions

From FlightGear wiki

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## General

Expressions are a feature of the SimGear library and provide a nice way of implementing complex math formulas using XML syntax.
They are supported in many systems within the FlightGear code.
**Beware:** Expressions do not check if your math creates floating point exceptions, like division by zero, square root of a negative number etc.

## Usage

Expressions are supported in

- Autopilot configuration files
- The particle system configuration files
- Animations (translate, rotate, scale, range, blend)
- The shader technique

## Sample Expressions

This is a sample expression for c = sqrt(a*a + b^2)

<expression> <sqrt> <sum> <product> <property>/value/a</property> <property>/value/a</property> </product> <pow> <property>/value/b</property> <value>2</value> </pow> </sum> </sqrt> </expression>

## Supported elements

<acos> <asin> <atan> <ceil> <cos> <cosh> <exp> <floor> <log> <log10> <rad2deg> <sin> <sinh> <sqrt> <tan> <tanh> <atan2> <div> <mod> <pow> <value> <property> <abs> (same as fabs) <sqr> <clip> <div> <mod> <sum> <difference> (same as dif) <product> (same as prod) <min> <max> <table>