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      <title>Maths</title>
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      <hr>
      <h4><a name="uk.ac.starlink.ttools.func.Maths">10.5.15 Maths</a></h4>
      <p>Standard mathematical and trigonometric functions.
         Trigonometric functions work with angles in radians.
      </p>
      <p>
         <dl>
            <dt><strong><code>sin( theta )</code></strong></dt>
            <dd>Sine of an angle.
               <ul>
                  <li><code>theta</code> <em>(floating point)</em>: an angle, in radians.
                  </li>
                  <li>return value <em>(floating point)</em>: the sine of the argument.
                  </li>
               </ul>
            </dd>
            <dt><strong><code>cos( theta )</code></strong></dt>
            <dd>Cosine of an angle.
               <ul>
                  <li><code>theta</code> <em>(floating point)</em>: an angle, in radians.
                  </li>
                  <li>return value <em>(floating point)</em>: the cosine of the argument.
                  </li>
               </ul>
            </dd>
            <dt><strong><code>tan( theta )</code></strong></dt>
            <dd>Tangent of an angle.
               <ul>
                  <li><code>theta</code> <em>(floating point)</em>: an angle, in radians.
                  </li>
                  <li>return value <em>(floating point)</em>: the tangent of the argument.
                  </li>
               </ul>
            </dd>
            <dt><strong><code>asin( x )</code></strong></dt>
            <dd>Arc sine of an angle. 
               The result is in the range of -<em>pi</em>/2 through
               <em>pi</em>/2.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: the value whose arc sine is to be returned.
                  </li>
                  <li>return value <em>(floating point)</em>: the arc sine of the argument (radians)
                  </li>
               </ul>
            </dd>
            <dt><strong><code>acos( x )</code></strong></dt>
            <dd>Arc cosine of an angle.  
               The result is in the range of 0.0 through <em>pi</em>.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: the value whose arc cosine is to be returned.
                  </li>
                  <li>return value <em>(floating point)</em>: the arc cosine of the argument (radians)
                  </li>
               </ul>
            </dd>
            <dt><strong><code>atan( x )</code></strong></dt>
            <dd>Arc tangent of an angle.
               The result is in the range of -<em>pi</em>/2 through <em>pi</em>/2.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: the value whose arc tangent is to be returned.
                  </li>
                  <li>return value <em>(floating point)</em>: the arc tangent of the argument (radians)
                  </li>
               </ul>
            </dd>
            <dt><strong><code>exp( x )</code></strong></dt>
            <dd>Euler's number <em>e</em> raised to a power.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: the exponent to raise <em>e</em> to.
                  </li>
                  <li>return value <em>(floating point)</em>: the value <em>e</em><sup>x</sup>,
                     where <em>e</em> is the base of the natural logarithms.
                  </li>
               </ul>
            </dd>
            <dt><strong><code>log10( x )</code></strong></dt>
            <dd>Logarithm to base 10.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: argument
                  </li>
                  <li>return value <em>(floating point)</em>: log<sub>10</sub>(x)
                  </li>
               </ul>
            </dd>
            <dt><strong><code>ln( x )</code></strong></dt>
            <dd>Natural logarithm.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: argument
                  </li>
                  <li>return value <em>(floating point)</em>: log<sub>e</sub>(x)
                  </li>
               </ul>
            </dd>
            <dt><strong><code>sqrt( x )</code></strong></dt>
            <dd>Square root.  
               The result is correctly rounded and positive.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: a value.
                  </li>
                  <li>return value <em>(floating point)</em>: the positive square root of <code>x</code>.
                     If the argument is NaN or less than zero, the result is NaN.
                  </li>
               </ul>
            </dd>
            <dt><strong><code>hypot( xs, ... )</code></strong></dt>
            <dd>Returns the square root of the sum of squares of its arguments.
               In the 2-argument case, doing it like this may avoid intermediate
               overflow or underflow.
               <ul>
                  <li><code>xs</code> <em>(floating point, one or more)</em>: one or more numeric values
                  </li>
                  <li>return value <em>(floating point)</em>: sqare root of sum of squares of arguments
                  </li>
               </ul>
            </dd>
            <dt><strong><code>atan2( y, x )</code></strong></dt>
            <dd>Converts rectangular coordinates (<code>x</code>,<code>y</code>)
               to polar (<code>r</code>,<code>theta</code>).
               This method computes the phase 
               <code>theta</code> by computing an arc tangent
               of <code>y/x</code> in the range of -<em>pi</em> to <em>pi</em>.
               <ul>
                  <li><code>y</code> <em>(floating point)</em>: the ordinate coordinate
                  </li>
                  <li><code>x</code> <em>(floating point)</em>: the abscissa coordinate
                  </li>
                  <li>return value <em>(floating point)</em>: the <code>theta</code> component (radians) of the point
                     (<code>r</code>,<code>theta</code>)
                     in polar coordinates that corresponds to the point
                     (<code>x</code>,<code>y</code>) in Cartesian coordinates.
                  </li>
               </ul>
            </dd>
            <dt><strong><code>pow( a, b )</code></strong></dt>
            <dd>Exponentiation. 
               The result is the value of the first argument raised to 
               the power of the second argument.
               <ul>
                  <li><code>a</code> <em>(floating point)</em>: the base.
                  </li>
                  <li><code>b</code> <em>(floating point)</em>: the exponent.
                  </li>
                  <li>return value <em>(floating point)</em>: the value <code>a<sup>b</sup></code>.
                  </li>
               </ul>
            </dd>
            <dt><strong><code>sinh( x )</code></strong></dt>
            <dd>Hyperbolic sine.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: parameter
                  </li>
                  <li>return value <em>(floating point)</em>: result
                  </li>
               </ul>
            </dd>
            <dt><strong><code>cosh( x )</code></strong></dt>
            <dd>Hyperbolic cosine.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: parameter
                  </li>
                  <li>return value <em>(floating point)</em>: result
                  </li>
               </ul>
            </dd>
            <dt><strong><code>tanh( x )</code></strong></dt>
            <dd>Hyperbolic tangent.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: parameter
                  </li>
                  <li>return value <em>(floating point)</em>: result
                  </li>
               </ul>
            </dd>
            <dt><strong><code>asinh( x )</code></strong></dt>
            <dd>Inverse hyperbolic sine.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: parameter
                  </li>
                  <li>return value <em>(floating point)</em>: result
                  </li>
               </ul>
            </dd>
            <dt><strong><code>acosh( x )</code></strong></dt>
            <dd>Inverse hyperbolic cosine.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: parameter
                  </li>
                  <li>return value <em>(floating point)</em>: result
                  </li>
               </ul>
            </dd>
            <dt><strong><code>atanh( x )</code></strong></dt>
            <dd>Inverse hyperbolic tangent.
               <ul>
                  <li><code>x</code> <em>(floating point)</em>: parameter
                  </li>
                  <li>return value <em>(floating point)</em>: result
                  </li>
               </ul>
            </dd>
            <dt><strong><code>E</code></strong></dt>
            <dd>Euler's number <em>e</em>, the base of natural logarithms.
               <ul></ul>
            </dd>
            <dt><strong><code>PI</code></strong></dt>
            <dd><em>Pi</em>, the ratio of the circumference of a circle to its diameter.
               <ul></ul>
            </dd>
            <dt><strong><code>Infinity</code></strong></dt>
            <dd>Positive infinite floating point value.
               <ul></ul>
            </dd>
            <dt><strong><code>NaN</code></strong></dt>
            <dd>Not-a-Number floating point value.
               Use with care; arithmetic and logical operations behave in strange
               ways near NaN (for instance, <code>NaN!=NaN</code>).
               For most purposes this is equivalent to the blank value.
               <ul></ul>
            </dd>
            <dt><strong><code>RANDOM</code></strong></dt>
            <dd>Evaluates to a random number in the range 0&lt;=x&lt;1.  
               This is different for each cell of the table.
               The quality of the randomness may not be particularly good.
               <ul></ul>
            </dd>
         </dl>
      </p>
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      <hr><i>STILTS - Starlink Tables Infrastructure Library Tool Set<br>Starlink User Note256<br>STILTS web page:
         <a href="http://www.starlink.ac.uk/stilts/">http://www.starlink.ac.uk/stilts/</a><br>Author email:
         <a href="mailto:m.b.taylor@bristol.ac.uk">m.b.taylor@bristol.ac.uk</a><br>Mailing list:
         <a href="mailto:topcat-user@jiscmail.ac.uk">topcat-user@jiscmail.ac.uk</a><br></i></body>
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