author Alpar Juttner Thu, 19 Jun 2008 17:33:06 +0100 changeset 351 2593e163e407 parent 350 b77fb8c32707 child 352 0badf3bb38c2 child 353 f8832dc16d45
 lemon/random.h file | annotate | diff | comparison | revisions
1.1 --- a/lemon/random.h	Thu Oct 23 12:39:39 2008 +0200
1.2 +++ b/lemon/random.h	Thu Jun 19 17:33:06 2008 +0100
1.3 @@ -840,6 +840,46 @@
1.4        return gauss()*std_dev+mean;
1.5      }
1.7 +    /// Lognormal distribution
1.8 +
1.9 +    /// Lognormal distribution. The parameters are the mean and the standard
1.10 +    /// deviation of <tt>exp(X)</tt>.
1.11 +    ///
1.12 +    double lognormal(double n_mean,double n_std_dev)
1.13 +    {
1.14 +      return std::exp(gauss(n_mean,n_std_dev));
1.15 +    }
1.16 +    /// Lognormal distribution
1.17 +
1.18 +    /// Lognormal distribution. The parameter is an <tt>std::pair</tt> of
1.19 +    /// the mean and the standard deviation of <tt>exp(X)</tt>.
1.20 +    ///
1.21 +    double lognormal(const std::pair<double,double> &params)
1.22 +    {
1.23 +      return std::exp(gauss(params.first,params.second));
1.24 +    }
1.25 +    /// Compute the lognormal parameters from mean and standard deviation
1.26 +
1.27 +    /// This function computes the lognormal parameters from mean and
1.28 +    /// standard deviation. The return value can direcly be passed to
1.29 +    /// lognormal().
1.30 +    std::pair<double,double> lognormalParamsFromMD(double mean,
1.31 +						   double std_dev)
1.32 +    {
1.33 +      double fr=std_dev/mean;
1.34 +      fr*=fr;
1.35 +      double lg=std::log(1+fr);
1.36 +      return std::pair<double,double>(std::log(mean)-lg/2.0,std::sqrt(lg));
1.37 +    }
1.38 +    /// Lognormal distribution with given mean and standard deviation
1.39 +
1.40 +    /// Lognormal distribution with given mean and standard deviation.
1.41 +    ///
1.42 +    double lognormalMD(double mean,double std_dev)
1.43 +    {
1.44 +      return lognormal(lognormalParamsFromMD(mean,std_dev));
1.45 +    }
1.46 +
1.47      /// Exponential distribution with given mean
1.49      /// This function generates an exponential distribution random number