# $ZARCTAN

## Synopsis

$ZARCTAN(n)

### Parameter

Argument | Description |
---|---|

n | Any positive or negative number. |

## Description

$ZARCTAN returns the trigonometric inverse (arc) tangent of n. Possible results range from 1.57079 (half of pi) through zero to –1.57079. The result is given in radians.

## Parameter

### n

Any positive or negative number. It can be specified as a value, a variable, or an expression. You can use the $ZPI special variable to specify pi. A non-numeric string is evaluated as 0.

The following are arc tangent values returned by $ZARCTAN:

2 | returns 1.107148717794090502 |

1 | returns .7853981633974483098 |

0 | returns 0 |

-1 | returns -.7853981633974483098 |

## Examples

The following example permits you to calculate the arc tangent of a number:

READ "Input a number: ",num WRITE !,"the arc tangent is: ",$ZARCTAN(num) QUIT

The following example compares the results from InterSystems IRIS fractional numbers ($DECIMAL numbers) and $DOUBLE numbers. In both cases, the arc tangent of pi/2 is a fractional number (not 1), but the arc tangent of 0 is 0:

WRITE !,"the arc tangent is: ",$ZARCTAN(0.0) WRITE !,"the arc tangent is: ",$ZARCTAN($DOUBLE(0.0)) WRITE !,"the arc tangent is: ",$ZARCTAN($ZPI) WRITE !,"the arc tangent is: ",$ZARCTAN($DOUBLE($ZPI)) WRITE !,"the arc tangent is: ",$ZARCTAN($ZPI/2) WRITE !,"the arc tangent is: ",$ZARCTAN($DOUBLE($ZPI)/2)