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Math::Trig(3pm)        Perl Programmers Reference Guide        Math::Trig(3pm)




NAME

       Math::Trig - trigonometric functions


SYNOPSIS

           use Math::Trig;

           $x = tan(0.9);
           $y = acos(3.7);
           $z = asin(2.4);

           $halfpi = pi/2;

           $rad = deg2rad(120);

           # Import constants pi2, pip2, pip4 (2*pi, pi/2, pi/4).
           use Math::Trig ':pi';

           # Import the conversions between cartesian/spherical/cylindrical.
           use Math::Trig ':radial';

               # Import the great circle formulas.
           use Math::Trig ':great_circle';


DESCRIPTION

       "Math::Trig" defines many trigonometric functions not defined by the
       core Perl which defines only the "sin()" and "cos()".  The constant pi
       is also defined as are a few convenience functions for angle
       conversions, and great circle formulas for spherical movement.


TRIGONOMETRIC FUNCTIONS

       The tangent

       tan

       The cofunctions of the sine, cosine, and tangent (cosec/csc and
       cotan/cot are aliases)

       csc, cosec, sec, sec, cot, cotan

       The arcus (also known as the inverse) functions of the sine, cosine,
       and tangent

       asin, acos, atan

       The principal value of the arc tangent of y/x

       atan2(y, x)

       The arcus cofunctions of the sine, cosine, and tangent (acosec/acsc and
       acotan/acot are aliases).  Note that atan2(0, 0) is not well-defined.

       acsc, acosec, asec, acot, acotan

       The hyperbolic sine, cosine, and tangent

       sinh, cosh, tanh

       The cofunctions of the hyperbolic sine, cosine, and tangent
       (cosech/csch and cotanh/coth are aliases)

       csch, cosech, sech, coth, cotanh

       The arcus (also known as the inverse) functions of the hyperbolic sine,
       cosine, and tangent

       asinh, acosh, atanh

       The arcus cofunctions of the hyperbolic sine, cosine, and tangent
       (acsch/acosech and acoth/acotanh are aliases)

       acsch, acosech, asech, acoth, acotanh

       The trigonometric constant pi and some of handy multiples of it are
       also defined.

       pi, pi2, pi4, pip2, pip4

       ERRORS DUE TO DIVISION BY ZERO

       The following functions

           acoth
           acsc
           acsch
           asec
           asech
           atanh
           cot
           coth
           csc
           csch
           sec
           sech
           tan
           tanh

       cannot be computed for all arguments because that would mean dividing
       by zero or taking logarithm of zero. These situations cause fatal
       runtime errors looking like this

           cot(0): Division by zero.
           (Because in the definition of cot(0), the divisor sin(0) is 0)
           Died at ...

       or

           atanh(-1): Logarithm of zero.
           Died at...

       For the "csc", "cot", "asec", "acsc", "acot", "csch", "coth", "asech",
       "acsch", the argument cannot be 0 (zero).  For the "atanh", "acoth",
       the argument cannot be 1 (one).  For the "atanh", "acoth", the argument
       cannot be "-1" (minus one).  For the "tan", "sec", "tanh", "sech", the
       argument cannot be pi/2 + k * pi, where k is any integer.

       Note that atan2(0, 0) is not well-defined.

       SIMPLE (REAL) ARGUMENTS, COMPLEX RESULTS

       Please note that some of the trigonometric functions can break out from
       the real axis into the complex plane. For example asin(2) has no
       definition for plain real numbers but it has definition for complex
       numbers.

       In Perl terms this means that supplying the usual Perl numbers (also
       known as scalars, please see perldata) as input for the trigonometric
       functions might produce as output results that no more are simple real
       numbers: instead they are complex numbers.

       The "Math::Trig" handles this by using the "Math::Complex" package
       which knows how to handle complex numbers, please see Math::Complex for
       more information. In practice you need not to worry about getting
       complex numbers as results because the "Math::Complex" takes care of
       details like for example how to display complex numbers. For example:

           print asin(2), "\n";

       should produce something like this (take or leave few last decimals):

           1.5707963267949-1.31695789692482i

       That is, a complex number with the real part of approximately 1.571 and
       the imaginary part of approximately "-1.317".


PLANE ANGLE CONVERSIONS

       (Plane, 2-dimensional) angles may be converted with the following
       functions.

       deg2rad
               $radians  = deg2rad($degrees);

       grad2rad
               $radians  = grad2rad($gradians);

       rad2deg
               $degrees  = rad2deg($radians);

       grad2deg
               $degrees  = grad2deg($gradians);

       deg2grad
               $gradians = deg2grad($degrees);

       rad2grad
               $gradians = rad2grad($radians);

       The full circle is 2 pi radians or 360 degrees or 400 gradians.  The
       result is by default wrapped to be inside the [0, {2pi,360,400}[
       circle.  If you don't want this, supply a true second argument:

           $zillions_of_radians  = deg2rad($zillions_of_degrees, 1);
           $negative_degrees     = rad2deg($negative_radians, 1);

       You can also do the wrapping explicitly by rad2rad(), deg2deg(), and
       grad2grad().

       rad2rad
               $radians_wrapped_by_2pi = rad2rad($radians);

       deg2deg
               $degrees_wrapped_by_360 = deg2deg($degrees);

       grad2grad
               $gradians_wrapped_by_400 = grad2grad($gradians);


RADIAL COORDINATE CONVERSIONS

       Radial coordinate systems are the spherical and the cylindrical
       systems, explained shortly in more detail.

       You can import radial coordinate conversion functions by using the
       ":radial" tag:

           use Math::Trig ':radial';

           ($rho, $theta, $z)     = cartesian_to_cylindrical($x, $y, $z);
           ($rho, $theta, $phi)   = cartesian_to_spherical($x, $y, $z);
           ($x, $y, $z)           = cylindrical_to_cartesian($rho, $theta, $z);
           ($rho_s, $theta, $phi) = cylindrical_to_spherical($rho_c, $theta, $z);
           ($x, $y, $z)           = spherical_to_cartesian($rho, $theta, $phi);
           ($rho_c, $theta, $z)   = spherical_to_cylindrical($rho_s, $theta, $phi);

       All angles are in radians.

       COORDINATE SYSTEMS

       Cartesian coordinates are the usual rectangular (x, y, z)-coordinates.

       Spherical coordinates, (rho, theta, pi), are three-dimensional
       coordinates which define a point in three-dimensional space.  They are
       based on a sphere surface.  The radius of the sphere is rho, also known
       as the radial coordinate.  The angle in the xy-plane (around the
       z-axis) is theta, also known as the azimuthal coordinate.  The angle
       from the z-axis is phi, also known as the polar coordinate.  The North
       Pole is therefore 0, 0, rho, and the Gulf of Guinea (think of the
       missing big chunk of Africa) 0, pi/2, rho.  In geographical terms phi
       is latitude (northward positive, southward negative) and theta is
       longitude (eastward positive, westward negative).

       BEWARE: some texts define theta and phi the other way round, some texts
       define the phi to start from the horizontal plane, some texts use r in
       place of rho.

       Cylindrical coordinates, (rho, theta, z), are three-dimensional
       coordinates which define a point in three-dimensional space.  They are
       based on a cylinder surface.  The radius of the cylinder is rho, also
       known as the radial coordinate.  The angle in the xy-plane (around the
       z-axis) is theta, also known as the azimuthal coordinate.  The third
       coordinate is the z, pointing up from the theta-plane.

       3-D ANGLE CONVERSIONS

       Conversions to and from spherical and cylindrical coordinates are
       available.  Please notice that the conversions are not necessarily
       reversible because of the equalities like pi angles being equal to -pi
       angles.

       cartesian_to_cylindrical
               ($rho, $theta, $z) = cartesian_to_cylindrical($x, $y, $z);

       cartesian_to_spherical
               ($rho, $theta, $phi) = cartesian_to_spherical($x, $y, $z);

       cylindrical_to_cartesian
               ($x, $y, $z) = cylindrical_to_cartesian($rho, $theta, $z);

       cylindrical_to_spherical
               ($rho_s, $theta, $phi) = cylindrical_to_spherical($rho_c, $theta, $z);

           Notice that when $z is not 0 $rho_s is not equal to $rho_c.

       spherical_to_cartesian
               ($x, $y, $z) = spherical_to_cartesian($rho, $theta, $phi);

       spherical_to_cylindrical
               ($rho_c, $theta, $z) = spherical_to_cylindrical($rho_s, $theta, $phi);

           Notice that when $z is not 0 $rho_c is not equal to $rho_s.


GREAT CIRCLE DISTANCES AND DIRECTIONS

       A great circle is section of a circle that contains the circle
       diameter: the shortest distance between two (non-antipodal) points on
       the spherical surface goes along the great circle connecting those two
       points.

       great_circle_distance

       You can compute spherical distances, called great circle distances, by
       importing the great_circle_distance() function:

         use Math::Trig 'great_circle_distance';

         $distance = great_circle_distance($theta0, $phi0, $theta1, $phi1, [, $rho]);

       The great circle distance is the shortest distance between two points
       on a sphere.  The distance is in $rho units.  The $rho is optional, it
       defaults to 1 (the unit sphere), therefore the distance defaults to
       radians.

       If you think geographically the theta are longitudes: zero at the
       Greenwhich meridian, eastward positive, westward negative--and the phi
       are latitudes: zero at the North Pole, northward positive, southward
       negative.  NOTE: this formula thinks in mathematics, not
       geographically: the phi zero is at the North Pole, not at the Equator
       on the west coast of Africa (Bay of Guinea).  You need to subtract your
       geographical coordinates from pi/2 (also known as 90 degrees).

         $distance = great_circle_distance($lon0, pi/2 - $lat0,
                                           $lon1, pi/2 - $lat1, $rho);

       great_circle_direction

       The direction you must follow the great circle (also known as bearing)
       can be computed by the great_circle_direction() function:

         use Math::Trig 'great_circle_direction';

         $direction = great_circle_direction($theta0, $phi0, $theta1, $phi1);

       great_circle_bearing

       Alias 'great_circle_bearing' for 'great_circle_direction' is also
       available.

         use Math::Trig 'great_circle_bearing';

         $direction = great_circle_bearing($theta0, $phi0, $theta1, $phi1);

       The result of great_circle_direction is in radians, zero indicating
       straight north, pi or -pi straight south, pi/2 straight west, and -pi/2
       straight east.

       You can inversely compute the destination if you know the starting
       point, direction, and distance:

       great_circle_destination

         use Math::Trig 'great_circle_destination';

         # thetad and phid are the destination coordinates,
         # dird is the final direction at the destination.

         ($thetad, $phid, $dird) =
           great_circle_destination($theta, $phi, $direction, $distance);

       or the midpoint if you know the end points:

       great_circle_midpoint

         use Math::Trig 'great_circle_midpoint';

         ($thetam, $phim) =
           great_circle_midpoint($theta0, $phi0, $theta1, $phi1);

       The great_circle_midpoint() is just a special case of

       great_circle_waypoint

         use Math::Trig 'great_circle_waypoint';

         ($thetai, $phii) =
           great_circle_waypoint($theta0, $phi0, $theta1, $phi1, $way);

       Where the $way is a value from zero ($theta0, $phi0) to one ($theta1,
       $phi1).  Note that antipodal points (where their distance is pi
       radians) do not have waypoints between them (they would have an an
       "equator" between them), and therefore "undef" is returned for
       antipodal points.  If the points are the same and the distance
       therefore zero and all waypoints therefore identical, the first point
       (either point) is returned.

       The thetas, phis, direction, and distance in the above are all in
       radians.

       You can import all the great circle formulas by

         use Math::Trig ':great_circle';

       Notice that the resulting directions might be somewhat surprising if
       you are looking at a flat worldmap: in such map projections the great
       circles quite often do not look like the shortest routes-- but for
       example the shortest possible routes from Europe or North America to
       Asia do often cross the polar regions.


EXAMPLES

       To calculate the distance between London (51.3N 0.5W) and Tokyo (35.7N
       139.8E) in kilometers:

           use Math::Trig qw(great_circle_distance deg2rad);

           # Notice the 90 - latitude: phi zero is at the North Pole.
           sub NESW { deg2rad($_[0]), deg2rad(90 - $_[1]) }
           my @L = NESW( -0.5, 51.3);
           my @T = NESW(139.8, 35.7);
           my $km = great_circle_distance(@L, @T, 6378); # About 9600 km.

       The direction you would have to go from London to Tokyo (in radians,
       straight north being zero, straight east being pi/2).

           use Math::Trig qw(great_circle_direction);

           my $rad = great_circle_direction(@L, @T); # About 0.547 or 0.174 pi.

       The midpoint between London and Tokyo being

           use Math::Trig qw(great_circle_midpoint);

           my @M = great_circle_midpoint(@L, @T);

       or about 89.16N 68.93E, practically at the North Pole.

       CAVEAT FOR GREAT CIRCLE FORMULAS

       The answers may be off by few percentages because of the irregular
       (slightly aspherical) form of the Earth.  The errors are at worst about
       0.55%, but generally below 0.3%.


BUGS

       Saying "use Math::Trig;" exports many mathematical routines in the
       caller environment and even overrides some ("sin", "cos").  This is
       construed as a feature by the Authors, actually... ;-)

       The code is not optimized for speed, especially because we use
       "Math::Complex" and thus go quite near complex numbers while doing the
       computations even when the arguments are not. This, however, cannot be
       completely avoided if we want things like asin(2) to give an answer
       instead of giving a fatal runtime error.

       Do not attempt navigation using these formulas.


AUTHORS

       Jarkko Hietaniemi <jhi!at!iki.fi> and Raphael Manfredi
       <Raphael_Manfredi!at!pobox.com>.



perl v5.10.0                      2007-12-18                   Math::Trig(3pm)

Mac OS X 10.6 - Generated Thu Sep 17 20:13:38 CDT 2009
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