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atan2 (3)
  • atan2 (3) ( Solaris man: Библиотечные вызовы )
  • >> atan2 (3) ( FreeBSD man: Библиотечные вызовы )
  • atan2 (3) ( Русские man: Библиотечные вызовы )
  • atan2 (3) ( Linux man: Библиотечные вызовы )
  • atan2 (3) ( POSIX man: Библиотечные вызовы )

  • BSD mandoc
     

    NAME

    
    
    atan2
    
     
    atan2f
    
     - arc tangent functions of two variables
    
     
    

    LIBRARY

    Lb libm
    
     
    

    SYNOPSIS

       #include <math.h>
    double atan2 (double y double x);
    float atan2f (float y float x);
     

    DESCRIPTION

    The atan2 ();
    and the atan2f ();
    functions compute the principal value of the arc tangent of Fa y/ Ns Ar x , using the signs of both arguments to determine the quadrant of the return value.  

    RETURN VALUES

    The atan2 ();
    and the atan2f ();
    functions, if successful, return the arc tangent of Fa y/ Ns Ar x in the range -words Bq - Ns , + Ns radians. Here are some of the special cases:

    Fn atan2 y x := Ta Fn atan y/x Ta if
    x > 0,
    Ta sign( y )*(
    atan (\*(Bay/x\*(Ba ) Ta);
    if x < 0,
    Ta 0 Ta if x = y = 0, or
    Ta sign( y )*\*(Pi/2 Ta if
    x = 0 != y

     

    NOTES

    The function atan2 ();
    defines "if x > 0," atan2 (0 0);
    = 0 despite that previously atan2 (0 0);
    may have generated an error message. The reasons for assigning a value to atan2 (0 0);
    are these:

    1. Programs that test arguments to avoid computing atan2 (0 0);
      must be indifferent to its value. Programs that require it to be invalid are vulnerable to diverse reactions to that invalidity on diverse computer systems.
    2. The atan2 ();
      function is used mostly to convert from rectangular (x,y) to polar (r,theta) coordinates that must satisfy x = r*cos theta and y = r*sin theta. These equations are satisfied when (x=0,y=0) is mapped to (r=0,theta=0). In general, conversions to polar coordinates should be computed thus:
      r       := hypot(x,y);  ... := sqrt(x*x+y*y)
      theta   := atan2(y,x).
      
    3. The foregoing formulas need not be altered to cope in a reasonable way with signed zeros and infinities on a machine that conforms to IEEE 754 the versions of hypot(3) and atan2 ();
      provided for such a machine are designed to handle all cases. That is why atan2 (±0 -0);
      = ± for instance. In general the formulas above are equivalent to these:
      r := sqrt(x*x+y*y); if r = 0 then x := copysign(1,x);

     

    SEE ALSO

    acos(3), asin(3), atan(3), cos(3), cosh(3), math(3), sin(3), sinh(3), tan(3), tanh(3)  

    STANDARDS

    The atan2 ();
    function conforms to St -isoC .


     

    Index

    NAME
    LIBRARY
    SYNOPSIS
    DESCRIPTION
    RETURN VALUES
    NOTES
    SEE ALSO
    STANDARDS


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