function mutated_nucleotide= Mutation(nucleotide,w,tt_ratio)
% Mutation  -  Mutates a given nucleotide with the Kimura 2-par model
%
% INPUT
% nucleotide	->	original nucleotide
% w 		->	edge length
% tt_ratio	-> 	transition-transversion ratio
%
% OUTPUT
% mutated_nucleotide  ->  nucleotide after mutation
%
% USAGE
% mutated_nucleotide= Mutation(nucleotide,w,tt_ratio)
%
% FUNCTION CALLS
% Kimura2P, SampleFromMultinomial


% ------------  Check for Errors  -------------
if nargin~=3
	error('Wrong number of input arguments')
end
if w<0 | tt_ratio<=0
	error('Parameters must be positive')
end
if sum([1 2 3 4]==nucleotide)~=1
	error('nucleotide nust be in {1,2,3,4}')
end

% ------ Matrix of nucleotide transition probabilities ------
nuc_trans_prob= Kimura2PM(w, tt_ratio);

% ------ New probabilties for the nucleotides -----
P_new= nuc_trans_prob(:,nucleotide);

% -- Mutation: Draw a new sample from the multinomial distribution --
mutated_nucleotide= SampleFromMultinomial(P_new);