[Issue 128410] New: ASIN and ACOS return ** Faulty expression **

[bu...@apache.org]

https://bz.apache.org/ooo/show_bug.cgi?id=128410

          Issue ID: 128410
        Issue Type: DEFECT
           Summary: ASIN and ACOS return  ** Faulty expression **
           Product: Writer
           Version: 4.1.7
          Hardware: PC
                OS: Windows 7
            Status: UNCONFIRMED
          Severity: Minor
          Priority: P5 (lowest)
         Component: ui
          Assignee: issues@openoffice.apache.org
          Reporter: czeslaw.wolanski@gmail.com
  Target Milestone: ---

Created attachment 86982
  --> https://bz.apache.org/ooo/attachment.cgi?id=86982&action=edit
File with formulas and relevant screenshots

In AOO Writer the following formulas:

=ASIN 1
=ASIN -1
=ACOS 1
=ACOS -1

return   ** Expression is faulty **

whereas in AOO Calc one can see the expected values i.e.

=ASIN(1)   returns   1.57... or  π/2 radians
=ASIN(-1)  returns  -1.57... or -π/2 radians
=ACOS(1)   returns   0
=ACOS(-1)  returns   3.14... or  π radians


Note:
Issue also observed in 4.2.0-dev

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[Issue 128410] ASIN and ACOS return ** Faulty expression **

[bu...@apache.org]

https://bz.apache.org/ooo/show_bug.cgi?id=128410

Regina Henschel <rb...@t-online.de> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |CONFIRMED
                 CC|                            |rb.henschel@t-online.de
     Ever confirmed|0                           |1

--- Comment #1 from Regina Henschel <rb...@t-online.de> ---
It is indeed wrong for argument 1. Workaround: Write the argument of asin as
0,999999999999999

Writer and Calc use different formula engines. To make Writer use the Calc
formula engine is such a large effort, that it is out of scope.

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[Issue 128410] ASIN and ACOS return ** Faulty expression **

[bu...@apache.org]

https://bz.apache.org/ooo/show_bug.cgi?id=128410

--- Comment #2 from Czesław Wolański <cz...@gmail.com> ---
(In reply to Regina Henschel from comment #1)
> It is indeed wrong for argument 1. Workaround: Write the argument of asin as
> 0,999999999999999
> 
> Writer and Calc use different formula engines. To make Writer use the Calc
> formula engine is such a large effort, that it is out of scope.

Thank you for the clarification and workaround.

It seems that one can get the right result using relationships among the
inverse trigonometric functions
( cf. https://en.wikipedia.org/wiki/Inverse_trigonometric_functions ).

The formulas for 1 / -1 argument are e.g.:

ASIN(1) = 2 * ATAN(1)
ASIN(-1) = 2 * ATAN(-1)
ACOS(1) = 2 * ATAN(0)
ACOS(-1) = π - ACOS(1)

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