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1 /* -*- c-basic-offset: 4 indent-tabs-mode: nil -*- vi:set ts=8 sts=4 sw=4: */
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2
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3 /*
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4 Sonic Visualiser
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5 An audio file viewer and annotation editor.
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6 Centre for Digital Music, Queen Mary, University of London.
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7 This file copyright 2006 Chris Cannam.
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8
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9 This program is free software; you can redistribute it and/or
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10 modify it under the terms of the GNU General Public License as
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11 published by the Free Software Foundation; either version 2 of the
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12 License, or (at your option) any later version. See the file
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13 COPYING included with this distribution for more information.
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14 */
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15
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16 #include "LogRange.h"
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17 #include "system/System.h"
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18
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19 #include <algorithm>
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20 #include <iostream>
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21 #include <cmath>
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22
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23 void
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24 LogRange::mapRange(double &min, double &max, double logthresh)
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25 {
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26 // ensure that max > min:
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27 if (min > max) std::swap(min, max);
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28 if (max == min) max = min + 1;
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29
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30 // cerr << "LogRange::mapRange: min = " << min << ", max = " << max << endl;
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31
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32 if (min >= 0.0) {
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33
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34 // and max > min, so we know min >= 0 and max > 0
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35
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36 max = log10(max);
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37
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38 if (min == 0.0) min = std::min(logthresh, max);
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39 else min = log10(min);
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40
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41 // cerr << "LogRange::mapRange: positive: min = " << min << ", max = " << max << endl;
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42
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43 } else if (max <= 0.0) {
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44
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45 // and max > min, so we know min < 0 and max <= 0
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46
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47 min = log10(-min);
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48
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49 if (max == 0.0) max = std::min(logthresh, min);
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50 else max = log10(-max);
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51
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52 std::swap(min, max);
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53
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54 // cerr << "LogRange::mapRange: negative: min = " << min << ", max = " << max << endl;
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55
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56 } else {
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57
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58 // min < 0 and max > 0
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59
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60 max = log10(std::max(max, -min));
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61 min = std::min(logthresh, max);
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62
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63 // cerr << "LogRange::mapRange: spanning: min = " << min << ", max = " << max << endl;
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64 }
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65
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66 if (min == max) min = max - 1;
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67 }
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68
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69 double
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70 LogRange::map(double value, double thresh)
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71 {
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72 if (value == 0.0) return thresh;
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73 return log10(fabs(value));
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74 }
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75
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76 double
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77 LogRange::unmap(double value)
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78 {
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79 return pow(10.0, value);
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80 }
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81
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82 static double
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83 sd(const std::vector<double> &values, int start, int n)
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84 {
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85 double sum = 0.0, mean = 0.0, variance = 0.0;
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86 for (int i = 0; i < n; ++i) {
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87 sum += values[start + i];
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88 }
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89 mean = sum / n;
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90 for (int i = 0; i < n; ++i) {
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91 double diff = values[start + i] - mean;
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92 variance += diff * diff;
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93 }
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94 variance = variance / n;
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95 return sqrt(variance);
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96 }
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97
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98 bool
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99 LogRange::useLogScale(std::vector<double> values)
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100 {
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101 // Principle: Partition the data into two sets around the median;
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102 // calculate the standard deviation of each set; if the two SDs
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103 // are very different, it's likely that a log scale would be good.
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104
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105 int n = int(values.size());
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106 if (n < 4) return false;
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107 std::sort(values.begin(), values.end());
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108 int mi = n / 2;
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109
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110 double sd0 = sd(values, 0, mi);
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111 double sd1 = sd(values, mi, n - mi);
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112
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113 SVDEBUG << "LogRange::useLogScale: sd0 = "
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114 << sd0 << ", sd1 = " << sd1 << endl;
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115
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116 if (sd0 == 0 || sd1 == 0) return false;
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117
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118 // I wonder what method of determining "one sd much bigger than
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119 // the other" would be appropriate here...
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120 if (std::max(sd0, sd1) / std::min(sd0, sd1) > 10.) return true;
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121 else return false;
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122 }
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123
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