To: J3                                                     J3/18-236
From:    Anton Shterenlikht
Subject: ACOSH result value error/typo
Date: 2018-August-02
References: N2159

Introduction:
~~~~~~~~~~~~~

[340] Clause 16.9.5 ACOSH( X ) p5 Result Value has:

"If the result is complex the imaginary part
is expressed in radians and lies in the range
0 <= AIMAG (ACOSH (X)) <= {pi}".
The lower bound must be {-pi}.

For reference see e.g. DLMF, Eqn. (4.37.16):
 https://dlmf.nist.gov/4.37#iv
which shows that the bounds for the imaginary
part of ACOSH are the same as for LOG,
i.e. between -pi and pi.

Edits to N2159
~~~~~~~~~~~~~~

[340] Clause 16.9.5 ACOSH( X ) p5 Result Value,
replace "0" with "{-pi}", so that the last
sentence of p5 reads as:

"If the result is complex the imaginary part
is expressed in radians and lies in the range
{-pi} <= AIMAG (ACOSH (X)) <= {pi}".

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