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| <title>The GNU Fortran Compiler: ATAN</title> |
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| <a name="ATAN-_002d_002d_002d-Arctangent-function"></a> |
| <h3 class="section">8.21 <code>ATAN</code> — Arctangent function</h3> |
| <a name="index-ATAN"></a> |
| <a name="index-DATAN"></a> |
| <a name="index-trigonometric-function_002c-tangent_002c-inverse"></a> |
| <a name="index-tangent_002c-inverse"></a> |
| |
| <dl compact="compact"> |
| <dt><em>Description</em>:</dt> |
| <dd><p><code>ATAN(X)</code> computes the arctangent of <var>X</var>. |
| </p> |
| </dd> |
| <dt><em>Standard</em>:</dt> |
| <dd><p>Fortran 77 and later, for a complex argument and for two arguments |
| Fortran 2008 or later |
| </p> |
| </dd> |
| <dt><em>Class</em>:</dt> |
| <dd><p>Elemental function |
| </p> |
| </dd> |
| <dt><em>Syntax</em>:</dt> |
| <dd><table> |
| <tr><td width="80%"><code>RESULT = ATAN(X)</code></td></tr> |
| <tr><td width="80%"><code>RESULT = ATAN(Y, X)</code></td></tr> |
| </table> |
| |
| </dd> |
| <dt><em>Arguments</em>:</dt> |
| <dd><table> |
| <tr><td width="15%"><var>X</var></td><td width="70%">The type shall be <code>REAL</code> or <code>COMPLEX</code>; |
| if <var>Y</var> is present, <var>X</var> shall be REAL.</td></tr> |
| <tr><td width="15%"><var>Y</var> shall be of the same type and kind as <var>X</var>.</td></tr> |
| </table> |
| |
| </dd> |
| <dt><em>Return value</em>:</dt> |
| <dd><p>The return value is of the same type and kind as <var>X</var>. |
| If <var>Y</var> is present, the result is identical to <code>ATAN2(Y,X)</code>. |
| Otherwise, it the arcus tangent of <var>X</var>, where the real part of |
| the result is in radians and lies in the range |
| <em>-\pi/2 \leq \Re \atan(x) \leq \pi/2</em>. |
| </p> |
| </dd> |
| <dt><em>Example</em>:</dt> |
| <dd><div class="smallexample"> |
| <pre class="smallexample">program test_atan |
| real(8) :: x = 2.866_8 |
| x = atan(x) |
| end program test_atan |
| </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>ATAN(X)</code></td><td width="20%"><code>REAL(4) X</code></td><td width="20%"><code>REAL(4)</code></td><td width="25%">Fortran 77 and later</td></tr> |
| <tr><td width="20%"><code>DATAN(X)</code></td><td width="20%"><code>REAL(8) X</code></td><td width="20%"><code>REAL(8)</code></td><td width="25%">Fortran 77 and later</td></tr> |
| </table> |
| |
| </dd> |
| <dt><em>See also</em>:</dt> |
| <dd><p>Inverse function: <a href="TAN.html#TAN">TAN</a> |
| </p> |
| </dd> |
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