j0(P)                                                     j0(P)





NAME
       j0, j1, jn - Bessel functions of the first kind

SYNOPSIS
       #include <math.h>

       double j0(double x);
       double j1(double x);
       double jn(int n, double x);



DESCRIPTION
       The  j0(), j1(), and jn() functions shall compute Bessel
       functions of x of the first kind of orders 0, 1, and  n,
       respectively.

       An  application  wishing  to  check for error situations
       should  set  errno   to   zero   and   call   feclearex-
       cept(FE_ALL_EXCEPT)  before calling these functions.  On
       return, if errno is non-zero or  fetestexcept(FE_INVALID
       |  FE_DIVBYZERO  |  FE_OVERFLOW  | FE_UNDERFLOW) is non-
       zero, an error has occurred.

RETURN VALUE
       Upon successful completion, these functions shall return
       the relevant Bessel value of x of the first kind.

       If the x argument is too large in magnitude, or the cor-
       rect result would cause underflow, 0 shall  be  returned
       and a range error may occur.

       If x is NaN, a NaN shall be returned.

ERRORS
       These functions may fail if:

       Range Error
              The  value of x was too large in magnitude, or an
              underflow occurred.

       If   the   integer   expression   (math_errhandling    &
       MATH_ERRNO)  is  non-zero,  then  errno  shall be set to
       [ERANGE]. If the integer expression (math_errhandling  &
       MATH_ERREXCEPT)  is  non-zero, then the underflow float-
       ing-point exception shall be raised.


       No other errors shall occur.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       On   error,   the   expressions   (math_errhandling    &
       MATH_ERRNO)  and (math_errhandling & MATH_ERREXCEPT) are
       independent of each other, but at least one of them must
       be non-zero.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       feclearexcept()  , fetestexcept() , isnan() , y0() , the
       Base Definitions volume of IEEE Std 1003.1-2001, Section
       4.18,  Treatment  of  Error  Conditions for Mathematical
       Functions, <math.h>

COPYRIGHT
       Portions of this text are reprinted  and  reproduced  in
       electronic  form  from  IEEE  Std  1003.1, 2003 Edition,
       Standard for Information Technology -- Portable  Operat-
       ing System Interface (POSIX), The Open Group Base Speci-
       fications Issue 6, Copyright (C) 2001-2003 by the Insti-
       tute  of  Electrical  and Electronics Engineers, Inc and
       The Open Group. In the event of any discrepancy  between
       this  version  and  the original IEEE and The Open Group
       Standard, the original IEEE and The Open Group  Standard
       is  the  referee  document. The original Standard can be
       obtained        online        at        http://www.open-
       group.org/unix/online.html .



POSIX                         2003                        j0(P)
