histogram - changed bin range computation

The bin range computation for the histogram showed bin limits at 4.999999
when 5.0 was expected. Added values with value 5.0 were therefore added
to the following bin. With this change the bin limits do not show the
rounding error. At least I could not reproduce the error that showed
up when using the routing from gsl_histogram_set_ranges_uniform.

diff --git a/src/math/histogram.c b/src/math/histogram.c
index e46986d2e0dff4ef6ba4a445cbc9c12aa34b7d0b..3f31ece4b17160804b149d06b6d6dd386cef9dc2 100644 (file)
--- a/src/math/histogram.c
+++ b/src/math/histogram.c
@@ -154,7 +154,27 @@ histogram_create (double bin_width_in, double min, double max)
 
   h->gsl_hist = gsl_histogram_alloc (bins);
 
-  gsl_histogram_set_ranges_uniform (h->gsl_hist, adjusted_min, adjusted_max);
+  /* The bin ranges could be computed with gsl_histogram_set_ranges_uniform,
+     but the number of bins is adapted to the ticks of the axis such that for example
+     data ranging from 1.0 to 7.0 with 6 bins will have bin limits at
+     2.0,3.0,4.0 and 5.0. Due to numerical accuracy the computed bin limits might
+     be 4.99999999 for a value which is expected to be 5.0. But the limits of
+     the histogram bins should be that what is expected from the displayed ticks.
+     Therefore the bin limits are computed from the rounded values which is similar
+     to the procedure at the chart_get_ticks_format. Actual bin limits should be
+     exactly what is displayed at the ticks.
+     But... I cannot reproduce the problem that I see with gsl_histogram_set_ranges_uniform
+     with the code below without rounding...
+  */
+  {
+    double *ranges = xmalloc (sizeof (double) * (bins + 1));
+    double interval = (adjusted_max - adjusted_min) / bins;
+    for (int i = 0; i < bins; i++)
+      ranges[i] = adjusted_min + interval * i;
+    ranges[bins] = adjusted_max;
+    gsl_histogram_set_ranges (h->gsl_hist, ranges, bins + 1);
+    free (ranges);
+  }
 
   stat = &h->parent;
   stat->accumulate = acc;