log_exp.cpp

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#include <itpp/base/math/log_exp.h>
#include <itpp/base/itcompat.h>

namespace itpp
{

// log-2 of the elements
vec log2(const vec &x) { return apply_function<double>(::log2, x); }
mat log2(const mat &x) { return apply_function<double>(::log2, x); }

// Safe substitute for <tt>log(exp(log_a) + exp(log_b))</tt>
double log_add(double log_a, double log_b)
{
  if (log_a < log_b) {
    double tmp = log_a;
    log_a = log_b;
    log_b = tmp;
  }
  double negdelta = log_b - log_a;
  if ((negdelta < log_double_min) || std::isnan(negdelta))
    return log_a;
  else
    return (log_a + log1p(std::exp(negdelta)));
}

}