
J0(P) POSIX Programmer's Manual 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
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 nonzero,
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 nonzero, then errno shall be
set to [ERANGE]. If the integer expression (math_errhandling & MATH_ERREXCEPT) is non
zero, then the underflow floatingpoint 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 nonzero.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
feclearexcept() , fetestexcept() , isnan() , y0() , the Base Definitions volume of
IEEE Std 1003.12001, Section 4.18, Treatment of Error Conditions for Mathematical Func
tions, <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) 20012003 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 orig
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 J0(P) 
