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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  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 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 .