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/* -*- c-basic-offset: 4 indent-tabs-mode: nil -*- vi:set ts=8 sts=4 sw=4: */
/*
Sonic Visualiser
An audio file viewer and annotation editor.
Centre for Digital Music, Queen Mary, University of London.
This file copyright 2006 Chris Cannam.
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License as
published by the Free Software Foundation; either version 2 of the
License, or (at your option) any later version. See the file
COPYING included with this distribution for more information.
*/
#include "LogRange.h"
#include "system/System.h"
#include <algorithm>
#include <iostream>
#include <cmath>
namespace sv {
void
LogRange::mapRange(double &min, double &max, double logthresh)
{
static double eps = 1e-10;
// ensure that max > min:
if (min > max) std::swap(min, max);
if (max == min) max = min + 1;
if (min >= 0.0) {
// and max > min, so we know min >= 0 and max > 0
max = log10(max);
if (min == 0.0) min = std::min(logthresh, max);
else min = log10(min);
} else if (max <= 0.0) {
// and max > min, so we know min < 0 and max <= 0
min = log10(-min);
if (max == 0.0) max = std::min(logthresh, min);
else max = log10(-max);
std::swap(min, max);
} else {
// min < 0 and max > 0
max = log10(std::max(max, -min));
min = std::min(logthresh, max);
}
if (fabs(max - min) < eps) min = max - 1;
}
double
LogRange::map(double value, double thresh)
{
if (value == 0.0) return thresh;
return log10(fabs(value));
}
double
LogRange::unmap(double value)
{
return pow(10.0, value);
}
static double
sd(const std::vector<double> &values, int start, int n)
{
double sum = 0.0, mean = 0.0, variance = 0.0;
for (int i = 0; i < n; ++i) {
sum += values[start + i];
}
mean = sum / n;
for (int i = 0; i < n; ++i) {
double diff = values[start + i] - mean;
variance += diff * diff;
}
variance = variance / n;
return sqrt(variance);
}
bool
LogRange::shouldUseLogScale(std::vector<double> values)
{
// Principle: Partition the data into two sets around the median;
// calculate the standard deviation of each set; if the two SDs
// are very different, it's likely that a log scale would be good.
int n = int(values.size());
if (n < 4) return false;
std::sort(values.begin(), values.end());
int mi = n / 2;
double sd0 = sd(values, 0, mi);
double sd1 = sd(values, mi, n - mi);
SVDEBUG << "LogRange::useLogScale: sd0 = "
<< sd0 << ", sd1 = " << sd1 << endl;
if (sd0 == 0 || sd1 == 0) return false;
// I wonder what method of determining "one sd much bigger than
// the other" would be appropriate here...
if (std::max(sd0, sd1) / std::min(sd0, sd1) > 10.) return true;
else return false;
}
} // end namespace sv
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