To: J3 J3/18-236r1
From: Anton Shterenlikht & Malcolm Cohen
Subject: ACOSH result value error/typo
Date: 2018-October-16
1. Introduction
As (a) the ACOSH function was in Fortran 2008, and
(b) the next revision is currently in FDIS ballot so too late to
change, unless that ballot fails,
this has become a Defect Report (aka Interpretation Request).
2. Interpretation Request
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NUMBER: F18/0001
TITLE: ACOSH principal value specification is wrong
KEYWORDS: ACOSH
DEFECT TYPE: Erratum
STATUS: J3 consideration in progress
QUESTION:
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}".
There is general agreement that the principal value of ACOSH should
have the real part non-negative which means the imaginary part must
range from -pi to +pi.
Is this a mistake in the definition of ACOSH?
ANSWER:
Yes, this is a mistake. Edits are included to correct this error.
EDITS to 18-007r1:
[340:34-35] 16.9.5 ACOSH, p5 Result Value,
after "is complex"
insert "the real part is non-negative and",
change "range 0" to "range $\pi$".
Making the whole p5 read
"Result Value. The result has a value equal to a processor-
dependent approximation to the inverse hyperbolic cosine
function of X. If the result is complex the real part if non-
negative and the imaginary part is expressed in radians and lies
in the range $-\pi$ <= AIMAG (ACOSH (X)) <= $\pi$."
SUBMITTED BY: Anton Shterenlikht
HISTORY: 18-236 m217 Submitted
18-236r1 m217 Put into interp format, revised edits.
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