<?xml version="1.0" encoding="utf-8"?><!DOCTYPE article  PUBLIC '-//OASIS//DTD DocBook XML V4.4//EN'  'http://www.docbook.org/xml/4.4/docbookx.dtd'><article><articleinfo><title>FAQ/atan</title><revhistory><revision><revnumber>8</revnumber><date>2013-03-08 10:17:28</date><authorinitials>localhost</authorinitials><revremark>converted to 1.6 markup</revremark></revision><revision><revnumber>7</revnumber><date>2012-07-09 13:37:00</date><authorinitials>PeterWatson</authorinitials><revremark>Revert to revision 3.</revremark></revision><revision><revnumber>6</revnumber><date>2012-07-07 17:54:07</date><authorinitials>190.7.31.11</authorinitials><revremark>ud35HF , [url=http://rkgavfvfqfsc.com/]rkgavfvfqfsc[/url], [link=http://apkitvqynjun.com/]apkitvqynjun[/link], http://mnzcitaguicy.com/</revremark></revision><revision><revnumber>5</revnumber><date>2012-07-07 17:53:30</date><authorinitials>216.77.162.166</authorinitials><revremark>ud35HF , [url=http://rkgavfvfqfsc.com/]rkgavfvfqfsc[/url], [link=http://apkitvqynjun.com/]apkitvqynjun[/link], http://mnzcitaguicy.com/</revremark></revision><revision><revnumber>4</revnumber><date>2012-07-05 12:26:40</date><authorinitials>65-118-31-232.dia.static.qwest.net</authorinitials><revremark>if u want to lose weight you have to run over 20 min and with a stlbae speed.Speed doesnt matter.If you cant run with 10 km/h thats fine.Go with 6km/h.I am overweight,i have 10 pounds more that i shou</revremark></revision><revision><revnumber>3</revnumber><date>2007-10-03 11:11:29</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>2</revnumber><date>2007-10-03 11:11:01</date><authorinitials>PeterWatson</authorinitials></revision><revision><revnumber>1</revnumber><date>2007-10-03 11:10:35</date><authorinitials>PeterWatson</authorinitials></revision></revhistory></articleinfo><section><title>Computing arctans in EXCEL</title><para>There are two functions which compute arc tangents (which computes the angle expressed in radians) of a line going from the origin to a co-ordinates in arrays X,Y. </para><para>Syntax: </para><para>P = atan2(Y,X) or P = atan(X/Y) </para><para>P = atan2(Y,X) returns an array P the same size as X and Y containing the element-by-element, four-quadrant inverse tangent (arctangent) of the real parts of Y and X. Any imaginary parts of the inputs are ignored. </para><para>Elements of P lie in the closed interval [-pi,pi], where pi is the MATLAB floating-point representation of $$\pi$$. atan uses sign(Y) and sign(X) to determine the specific quadrant. </para><para>atan2(Y,X) contrasts with atan(Y/X), <emphasis role="strong">whose results are limited to the interval [-pi/2, pi/2]</emphasis>. </para></section></article>