X-Git-Url: https://pintos-os.org/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=src%2Fmath%2Fhistogram.c;h=8aaa16f9e0a684bca8333fee51d6c6874319a69b;hb=40c169c1409b0f16e6ee8f0ceaa0ce6937c90a5c;hp=b00067210f08676736d589660c9eb85f75216831;hpb=fa1fffd5c789d9c7875fc3bdf556eaf017cf524e;p=pspp diff --git a/src/math/histogram.c b/src/math/histogram.c index b00067210f..8aaa16f9e0 100644 --- a/src/math/histogram.c +++ b/src/math/histogram.c @@ -58,162 +58,83 @@ destroy (struct statistic *s) } -static -double get_slack (double limit, double half_bin_width, int *n_half_bins) -{ - double ipart, remainder; - - assert (half_bin_width > 0); - - remainder = modf (limit / half_bin_width, &ipart); - - /* In C modf and % behave in an unexpected (to me at any rate) manner - when presented with a negative value - - For example, modf (-7.0 / 3.0) returns -2.0 R -0.3333 - */ - - - *n_half_bins = ipart; - - return remainder * half_bin_width; -} - - -/* This functions adjusts the upper and lower range of the histogram to make them fit BIN_WIDTH - MIN and MAX are the lowest and highest data to be plotted in the histogram. - ADJ_MIN and ADJ_MAX are locations of the adjusted values of MIN and MAX (the range will - always be equal or slightly larger). - Returns the number of bins. - - The "testing_assert" expressions in this function should be algebraically correct. - However, due to floating point rounding they could fail, especially when small numbers - are involved. In normal use, therefore, testing_assert does nothing. - */ +/* Find a bin width which is adapted to the scaling of the x axis +In the example here, the binwidth is half of the tick interval. + + binwidth + > < + |....+....+....+. .+....| + LOWER 1 2 3 N_TICKS + ^LOWDBL ^HIGHDBL + +This only works, when the min and max value for the histogram are adapted +such that (max-min) is a multiple of the binwidth. Then the location of the +first bin has to be aligned to the ticks. +*/ static int -adjust_bin_ranges (double bin_width, double min, double max, double *adj_min, double *adj_max) +hist_find_pretty_no_of_bins(double bin_width_in, double min, double max, + double *adjusted_min, double *adjusted_max) { - const double half_bin_width = bin_width / 2.0; + double lower, interval; + int n_ticks; + double binwidth; + int nbins; - /* The lower and upper limits of the histogram, in units of half - bin widths */ - int lower_limit, upper_limit; + chart_get_scale (max, min, &lower, &interval, &n_ticks); - double lower_slack = get_slack (min, half_bin_width, &lower_limit); - double upper_slack = -get_slack (max, half_bin_width, &upper_limit); - - testing_assert (max > min); - - /* If min is negative, then lower_slack may be less than zero. - In this case, the lower bound must be extended in the negative direction - so that it is less than OR EQUAL to min. - */ - if (lower_slack < 0) + if (bin_width_in >= 2 * interval) { - lower_limit--; - lower_slack += half_bin_width; + binwidth = floor(bin_width_in/interval) * interval; + *adjusted_min = lower; } - testing_assert (lower_limit * half_bin_width <= min); - - /* However, the upper bound must be extended regardless, because histogram bins - span the range [lower, upper). In other words, the upper bound must be - greater than max. - */ - upper_limit++;; - upper_slack += half_bin_width; - testing_assert (upper_limit * half_bin_width > max); - - /* The range must be an EVEN number of half bin_widths */ - if ( (upper_limit - lower_limit) % 2) + else if (bin_width_in >= 1.5 * interval) { - /* Extend the range at the end which gives the least unused space */ - if (upper_slack > lower_slack) - { - lower_limit--; - lower_slack += half_bin_width; - } + binwidth = 1.5 * interval; + if (min < (lower + 0.5 * interval)) + *adjusted_min = lower; else - { - upper_limit++; - upper_slack += half_bin_width; - } + *adjusted_min = lower + 0.5 * interval; } - - /* But the range should be aligned to an ODD number of - half bin widths, so that the labels are aesthetically pleasing ones. - Otherwise we are likely to get labels such as -3 -1 1 3 instead of -2 0 2 4 - */ - if ( lower_limit % 2 == 0) + else if (bin_width_in >= interval) { - /* If there is not enough slack at either end to perform a shift, - then we must extend the range so that there is. We must extend - by two half bin widths in order to preserve the EVEN condition - established above. Also, we extend on the end with the least - slack, in order to keep things as balanced as possible. */ - if ( upper_slack > lower_slack && upper_slack <= half_bin_width) - { - lower_limit -= 2; - lower_slack += 2 * half_bin_width; - } - - if (lower_slack > upper_slack && lower_slack < half_bin_width) - { - upper_limit += 2; - upper_slack += 2 * half_bin_width; - } - - if (upper_slack > lower_slack) - { - testing_assert (upper_slack > half_bin_width); - - /* Adjust the range to the left */ - lower_limit --; - upper_limit --; - upper_slack -= half_bin_width; - lower_slack += half_bin_width; - } - else - { - testing_assert (lower_slack >= half_bin_width); - - /* Adjust the range to the right */ - lower_limit ++; - upper_limit ++; - lower_slack -= half_bin_width; - upper_slack += half_bin_width; - } + binwidth = interval; + *adjusted_min = lower; } - - /* If there are any completely empty bins, then remove them, - since empty bins don't really add much information to the histogram. - */ - if (upper_slack > 2 * half_bin_width) + else if (bin_width_in >= (2.0/3.0 * interval)) { - upper_slack -= 2 * half_bin_width; - upper_limit -=2; + binwidth = (2.0/3.0 * interval); + if (min >= lower + binwidth) + *adjusted_min = lower + binwidth; + else + *adjusted_min = lower; } - - if (lower_slack >= 2 * half_bin_width) + else { - lower_slack -= 2 * half_bin_width; - lower_limit +=2; + int i; + for(i = 2; bin_width_in < interval/i; i++); + binwidth = interval/i; + *adjusted_min = floor((min - lower)/binwidth)*binwidth + lower; } - *adj_min = lower_limit * half_bin_width; - *adj_max = upper_limit * half_bin_width; + nbins = ceil((max-*adjusted_min)/binwidth); + *adjusted_max = nbins*binwidth + *adjusted_min; - testing_assert (*adj_max > max); - testing_assert (*adj_min <= min); + /* adjusted_max should never be smaller than max but if it is equal + then the gsl_histogram will not add the cases which have max value */ + if (*adjusted_max <= max) + { + *adjusted_max += binwidth; + nbins++; + } + assert (*adjusted_min <= min); - return (upper_limit - lower_limit) / 2.0; + return nbins; } - struct histogram * -histogram_create (double bin_width, double min, double max) +histogram_create (double bin_width_in, double min, double max) { - const int MAX_BINS = 25; struct histogram *h; struct statistic *stat; int bins; @@ -225,28 +146,35 @@ histogram_create (double bin_width, double min, double max) return NULL; } - assert (bin_width > 0); + assert (bin_width_in > 0); - bin_width = chart_rounded_tick (bin_width); - bins = adjust_bin_ranges (bin_width, min, max, &adjusted_min, &adjusted_max); - - /* Force the number of bins to lie in a sensible range. */ - if (bins > MAX_BINS) - { - bin_width = chart_rounded_tick ((max - min) / (double) (MAX_BINS - 1)); - bins = adjust_bin_ranges (bin_width, - min, max, &adjusted_min, &adjusted_max); - } - - /* Can this ever happen? */ - if (bins < 1) - bins = 1; + bins = hist_find_pretty_no_of_bins(bin_width_in, min, max, &adjusted_min, &adjusted_max); h = xmalloc (sizeof *h); 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;