%   [m,T]=Ret_periodGRU(Md,Mu,dM,Mmin,lamb,eps,b)
%
% EVALUATES THE MEAN RETURN PERIOD VALUES USING THE UNLIMITED G-R LED 
%   MAGNITUDE DISTRIBUTION MODEL.
%
% AUTHOR: S. Lasocki 06/2014 within IS-EPOS project.
%
% DESCRIPTION: The assumption on the unlimited Gutenberg-Richter relation 
% leads to the exponential distribution model of magnitude distribution 
% from and above the catalog completness level Mmin. The shape parameter of 
% this distribution and consequently the G-R b-value are calculated at 
% start-up of the stationary hazard assessment services in the
% unlimited Gutenberg-Richter estimation mode.
%
% The mean return period of magnitude M is the average elapsed time between
% the consecutive earthquakes of magnitude M.   
% The mean return periods are calculated for magnitude starting from Md up
% to Mu with step dM.
% 
%INPUT:
%   Md - starting magnitude for return period calculations
%   Mu - ending magnitude for return period calculations
%   dM - magnitude step for return period calculations 
%   Mmin - lower bound of the distribution - catalog completeness level
%   lamb - mean activity rate for events M>=Mmin
%   eps - length of the round-off interval of magnitudes.
%   b - Gutenberg-Richter b-value
%
%OUTPUT:
%   m - vector of independent variable (magnitude) m=(Md:dM:Mu)
%   T - vector od mean return periods of the same length as m
%
% LICENSE
%     This file is a part of the IS-EPOS e-PLATFORM.
%
%     This 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 3 of the License, or 
%     (at your option) any later version.
% 
%     This program is distributed in the hope that it will be useful,
%     but WITHOUT ANY WARRANTY; without even the implied warranty of
%     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
%     GNU General Public License for more details.
% 

function [m,T]=Ret_periodGRU(Md,Mu,dM,Mmin,lamb,eps,b)

% -------------- VALIDATION RULES -------------  K_21NOV2016
 if dM<=0;error('Magnitude Step must be greater than 0');end
%----------------------------------------------------------

if Md<Mmin; Md=Mmin;end
m=(Md:dM:Mu)';
beta=b*log(10);
T=1/lamb./exp(-beta*(m-Mmin+eps/2));
end