Unidentified subject!

[John W. Eaton]

On 17-May-2000, I wrote:
| 
| On 17-May-2000, address@hidden <address@hidden> wrote:
| 
| | Hello! 
| | 
| | What is the MAIN reason that 1.8:0.05:1.9 produces [1.8000 1.8500]
| | and not [1.8000 1.8500 1.9000]? 
| | I am using 2.0.14 version of Octave. 
| | Thank you for your answer. 
| | Best regards,
| | Emil Zagar
| 
| I'd guess that the MAIN reason is that there is a bug in the way
| Octave is trying (very hard) to compute the correct number of elements
| for ranges.  If you're in a debugging mood, the code to look at is in
| the Range::nelem_internal and related functions in liboctave/Range.cc.

Here is a patch (against the 2.1.x sources, but it should be obvious
how to apply it to the older sources as well) that should fix this
problem.  With it, here is what I see:

  GNU Octave, version 2.1.32 (i686-pc-linux-gnu).
  Copyright (C) 1996, 1997, 1998, 1999, 2000 John W. Eaton.
  This is free software with ABSOLUTELY NO WARRANTY.
  For details, type `warranty'.

  octave:1> 1.8:0.05:1.9
  ans =

    1.8000  1.8500  1.9000

  octave:2> 1.0008:0.00005:1.0009
  ans =

    1.0008  1.0009  1.0009



It is a more than a little bit embarrassing to me that this bug has
been in Octave for so long.

Thanks,

jwe


2000-12-09  John W. Eaton  <address@hidden>

        * Range.cc (Range::nelem_internal): Call round here, not tfloor.
        Rename n_intervals to be n_elt.


Index: Range.cc
===================================================================
RCS file: /usr/local/cvsroot/octave/liboctave/Range.cc,v
retrieving revision 1.24
diff -u -r1.24 Range.cc
--- Range.cc    2000/02/01 10:06:59     1.24
+++ Range.cc    2000/12/10 05:44:16
@@ -235,11 +235,11 @@
 {
   double ct = 3.0 * DBL_EPSILON;
 
-  double tmp = tfloor ((rng_limit - rng_base + rng_inc) / rng_inc, ct);
+  double tmp = round ((rng_limit - rng_base + rng_inc) / rng_inc, ct);
 
-  int n_intervals = (tmp > 0.0 ? static_cast<int> (tmp) : 0);
+  int n_elt = (tmp > 0.0 ? static_cast<int> (tmp) : 0);
 
-  return (n_intervals >= INT_MAX - 1) ? -1 : n_intervals;
+  return (n_elt >= INT_MAX - 1) ? -1 : n_elt;
 }
 
 /*



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