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(doublex); double j1(doublex); double jn(intn, doublex);

# 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 POSIX.1‐2017, *Section
4.20*, *Treatment of Error Conditions for Mathematical Functions*,
**<math.h>**

# COPYRIGHT

Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

2017 | IEEE/The Open Group |