J0(3POSIX)

💖 J0 — the POSIX girlies' manual, page 3POSIX 💖

okay so bestie, this is J0(3POSIX) from the POSIX Programmer's Manual, and we are about to get so cozy with some Bessel functions. 🎀

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🌸 PROLOG 🌸

Real talk first: this page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (so like, go check the corresponding Linux manual page for the deets on Linux behavior), or honestly the interface might not even be implemented on Linux at all. 💀

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✨ NAME ✨

j0, j1, jn — Bessel functions of the first kind. yes queen, we're doing math. 🧚

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🦋 SYNOPSIS 🦋

#include <math.h>

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

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💅 DESCRIPTION 💅

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

And if your application wants to check for error situations (very responsible of you, love that), you should set errno to zero and call feclearexcept(FE_ALL_EXCEPT) before calling these functions. Then on return, if errno is non-zero, or if fetestexcept(FE_INVALID | FE_DIVBYZERO | FE_OVERFLOW | FE_UNDERFLOW) is non-zero — boom, an error has occurred. no cap. 🌈

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👑 RETURN VALUE 👑

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

If the x argument is too large in magnitude, or the correct result would cause underflow, then 0 shall be returned and a range error may occur. (underflow era, not cute.)

If x is NaN, a NaN shall be returned. it's giving "you get back what you put in" fr fr. 🫶

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💀 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]. And 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. periodt.

The following sections are informative. (translation: the tea is optional but we're still reading it 💖)

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🍓 EXAMPLES 🍓

None. (yes really, nothing, the void, empty, we move.)

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🎀 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. they don't need to match, they just both gotta show up to the function. 😌

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⭐ RATIONALE ⭐

None. (the reasoning? not here bestie, we simply don't have one. 🦋)

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🔥 FUTURE DIRECTIONS 🔥

None. (the future? unclear. we live in the present. 💅)

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🌸 SEE ALSO 🌸

• feclearexcept()
• fetestexcept()
• isnan()
• y0()

And from the Base Definitions volume of POSIX.1‐2017: Section 4.20, Treatment of Error Conditions for Mathematical Functions, and <math.h>. iykyk. ✨

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💜 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 .

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bestie if anything here looks weird, blame the file conversion, not the math girlies 🫶

and that's the whole page!! mwah 💋 — brought to you by IEEE/The Open Group, 2017, signing off on J0(3POSIX). stay mathematically gorgeous. 💖✨🎀