bugGNU Octave - Bugs: bug #65508, [octave forge] (mapping)...

 
 

bug #65508: [octave forge] (mapping) degrees2dm inaccuracy

Submitter:  None
Submitted:  Fri 22 Mar 2024 03:30:00 PM UTC
   
 
Category:  Octave Package Severity:  3 - Normal
Priority:  5 - Normal Item Group:  Inaccurate Result
Status:  None Assigned to:  philipnienhuis
Originator Name:  Originator Email:  -email is unavailable-
Open/Closed:  * Open Release:  * other
Operating System:  * Any Fixed Release:  None
Planned Release:  None
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Fri 22 Mar 2024 08:46:14 PM UTC, comment #1: 

Thanks for this contribution.
I'll have a look, see also what I wrote in bug #65291.

Philip Nienhuis <philipnienhuis>
Group Member
Fri 22 Mar 2024 03:30:00 PM UTC, original submission:  

This is somewhat related to bug #65291 and I am the same "Anonymous" as has been posting there.

The degrees2dm function in the mapping package from https://sourceforge.net/p/octave/mapping/ci/default/tree/inst/degrees2dm.m has some accuracy issues.  For example, degrees2dm(realmax()) returns [realmax(), NaN] instead of [realmax(), 0], and degrees2dm (2e14 + 0.25) returns [2e14, 16] instead of [2e14, 15].

Attached is a version of degrees2dm.m with the following changes:

  • Documentation:
    • Specify that the minutes component will always have magnitude less than 60.
    • Adjust the first example to make everything exact and to demonstrate fractional minutes.
    • Remove the second example which was incorrect and is now redundant.
    • Correct a variable name mismatch in the last example.
    • Remove the negative sign (which does not seem to be displayed by default) from a zero in the result in the last example.
  • Implementation:
    • Reject non-real input.
    • Add special handling for char and logical input to improve performance and clarity.
    • Change the computation of the minutes to improve accuracy.  It should now always return the correctly rounded result (assuming fix(), subtraction, and multiplication are correctly rounded, which I expect is true).
      • Overflow for large inputs is avoided.
      • Minutes now depend only on the fractional part of the input.
      • Possible issues are avoided by not using the rem function.  Documentation for rem claims that "values within a few eps of an integer will be rounded to that integer before computation for compatibility with MATLAB", but I have failed to verify this.
    • Update the sign-flipping logic to account for the change to the computation of the minutes, and hopefully improve clarity.
    • Reject input types not explicitly handled.
      • This might be unreachable currently, but is intended to prevent applying the function to types where it hasn't been validated.  Not sure this is a good idea.
  • Tests:
    • Add tests which fail with the existing implementation.
    • Add tests which do not fail with the existing implementation, but do help demonstrate correctness.
  • Other:
    • Add `## Copyright (C) 2024 The Octave Project Developers` because I am offering this contribution anonymously.


Anonymous

 

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Attached Files
file #55880:  degrees2dm.m added by None (5KiB - application/octet-stream)

 

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Follow 2 latest changes.

Date Changed by Updated Field Previous Value => Replaced by
2024-03-22 philipnienhuis Assigned toNone philipnienhuis
2024-03-22 None Attached File- Added degrees2dm.m, #55880

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