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J0(3P)                     POSIX Programmer's Manual                    J0(3P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the  corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.
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  feclearexcept(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  correct  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
       floating-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 Condi-
       tions 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  Operating  System  Interface (POSIX), The Open Group Base
       Specifications Issue 6, Copyright (C) 2001-2003  by  the  Institute  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.opengroup.org/unix/online.html .

IEEE/The Open Group                  2003                               J0(3P)