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| <title>The GNU Fortran Compiler: ATAN2</title> |
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| Next: <a href="ATANH.html#ATANH" accesskey="n" rel="next">ATANH</a>, Previous: <a href="ATAN.html#ATAN" accesskey="p" rel="prev">ATAN</a>, Up: <a href="Intrinsic-Procedures.html#Intrinsic-Procedures" accesskey="u" rel="up">Intrinsic Procedures</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p> |
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| <a name="ATAN2-_002d_002d_002d-Arctangent-function"></a> |
| <h3 class="section">8.22 <code>ATAN2</code> — Arctangent function</h3> |
| <a name="index-ATAN2"></a> |
| <a name="index-DATAN2"></a> |
| <a name="index-trigonometric-function_002c-tangent_002c-inverse-1"></a> |
| <a name="index-tangent_002c-inverse-1"></a> |
| |
| <dl compact="compact"> |
| <dt><em>Description</em>:</dt> |
| <dd><p><code>ATAN2(Y, X)</code> computes the principal value of the argument |
| function of the complex number <em>X + i Y</em>. This function can |
| be used to transform from Cartesian into polar coordinates and |
| allows to determine the angle in the correct quadrant. |
| </p> |
| </dd> |
| <dt><em>Standard</em>:</dt> |
| <dd><p>Fortran 77 and later |
| </p> |
| </dd> |
| <dt><em>Class</em>:</dt> |
| <dd><p>Elemental function |
| </p> |
| </dd> |
| <dt><em>Syntax</em>:</dt> |
| <dd><p><code>RESULT = ATAN2(Y, X)</code> |
| </p> |
| </dd> |
| <dt><em>Arguments</em>:</dt> |
| <dd><table> |
| <tr><td width="15%"><var>Y</var></td><td width="70%">The type shall be <code>REAL</code>.</td></tr> |
| <tr><td width="15%"><var>X</var></td><td width="70%">The type and kind type parameter shall be the same as <var>Y</var>. |
| If <var>Y</var> is zero, then <var>X</var> must be nonzero.</td></tr> |
| </table> |
| |
| </dd> |
| <dt><em>Return value</em>:</dt> |
| <dd><p>The return value has the same type and kind type parameter as <var>Y</var>. It |
| is the principal value of the complex number <em>X + i Y</em>. If <var>X</var> |
| is nonzero, then it lies in the range <em>-\pi \le \atan (x) \leq \pi</em>. |
| The sign is positive if <var>Y</var> is positive. If <var>Y</var> is zero, then |
| the return value is zero if <var>X</var> is strictly positive, <em>\pi</em> if |
| <var>X</var> is negative and <var>Y</var> is positive zero (or the processor does |
| not handle signed zeros), and <em>-\pi</em> if <var>X</var> is negative and |
| <var>Y</var> is negative zero. Finally, if <var>X</var> is zero, then the |
| magnitude of the result is <em>\pi/2</em>. |
| </p> |
| </dd> |
| <dt><em>Example</em>:</dt> |
| <dd><div class="smallexample"> |
| <pre class="smallexample">program test_atan2 |
| real(4) :: x = 1.e0_4, y = 0.5e0_4 |
| x = atan2(y,x) |
| end program test_atan2 |
| </pre></div> |
| |
| </dd> |
| <dt><em>Specific names</em>:</dt> |
| <dd><table> |
| <tr><td width="20%">Name</td><td width="20%">Argument</td><td width="20%">Return type</td><td width="25%">Standard</td></tr> |
| <tr><td width="20%"><code>ATAN2(X, Y)</code></td><td width="20%"><code>REAL(4) X, Y</code></td><td width="20%"><code>REAL(4)</code></td><td width="25%">Fortran 77 and later</td></tr> |
| <tr><td width="20%"><code>DATAN2(X, Y)</code></td><td width="20%"><code>REAL(8) X, Y</code></td><td width="20%"><code>REAL(8)</code></td><td width="25%">Fortran 77 and later</td></tr> |
| </table> |
| </dd> |
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