bugPSPP - Bugs: bug #25099, Floating Origin Needed

 
 

bug #25099: Floating Origin Needed

Submitter:  John Darrington <jmd>
Submitted:  Mon 15 Dec 2008 10:59:48 AM UTC
   
 
Category:  Graphical User Interface Severity:  5 - Average
Status:  Fixed Assigned to:  None
Open/Closed:  Closed Release:  None
Effort:  0.00
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Tue 10 Mar 2009 07:27:53 AM UTC, comment #4: 

Oops! How embarrasing! There were some places where I'd used float  instead of double.

Thanks for opening my eyes Ben.  I should have done the numerical analysis before diagnosing the problem.

I've pushed a fix and closing this item.

John Darrington <jmd>
Group administrator
Tue 10 Mar 2009 06:26:16 AM UTC, comment #3: 

Presumably this occurs due to the inaccuracy of large integers when represented as doubles.  But a 64-bit IEEE double can represent any integer up to 9,007,199,254,740,992 (2**53) without loss of precision, which is much larger than 10**7 < 2**24.  Where are our 29 binary orders of magnitude going?

Ben Pfaff <blp>
Group administrator
Tue 10 Mar 2009 05:57:33 AM UTC, comment #2: 

Screenshot of what it looks like attached.


Ben Pfaff <blp>
Group administrator
Tue 10 Mar 2009 05:54:10 AM UTC, comment #1: 

I had to use more than 1,000,000 cases to see this effect.  Here is a program that generates an appropriate data file:


INPUT PROGRAM.
        LOOP #I=1 TO 1e7.
                COMPUTE X=NORMAL(10).
                END CASE.
        END LOOP.
        END FILE.
END INPUT PROGRAM.
save outfile='big.sav'.
execute.


Ben Pfaff <blp>
Group administrator
Mon 15 Dec 2008 10:59:48 AM UTC, original submission:  

When viewing a dataset with very large numbers of cases
 ( > 500,000) the cell boundaries become unstable.

This is the classic "floating origin" problem.  Its cause and solution is described at http://floatingorigin.com

John Darrington <jmd>
Group administrator

 

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Attached Files
file #17637:  foo.png added by blp (35KiB - image/png)

 

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    Follow 3 latest changes.

    Date Changed by Updated Field Previous Value => Replaced by
    2009-03-10 jmd StatusNone Fixed
        Open/ClosedOpen Closed
    2009-03-10 blp Attached File- Added foo.png, #17637

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