function [upcovar,upmu] = updatecov(data,covar,mu,addrow,delrow,option)
% This function updates the mean and covariance matrix of the full data
% after adding or removing observations.
%
% Input arguments:
% data : the original data
% covar : the covariance matrix of the data
% mu : the center of the data
% addrow : matrix with contains the measurements of the data points that are added.
% delrow : indices of the data points that are removed from the data set.
% option : indicates whether you want to remove or add an observation.
% 0 : remove
% 1 : add
% 2 : change a row with another vector. The row that had to be changed has to be put in
% delrow. The vector that needs to be add has to be put in addrow.
n = size(data,1);
if option == 0
for i = 1:length(delrow)
j = delrow(i);
mu = (n-i+1)/(n - i)*(mu - 1/(n - i + 1)*data(j,:));
covar = (n - i)/(n - i -1)*covar - (n - i)/((n - i + 1)*(n-i-1))*((mu - data(j,:))'*(mu - data(j,:)));
end
upmu = mu;
upcovar = covar;
elseif option == 1
for i = 1:size(addrow,1)
covar = (n+i-2)/(n +i-1)*covar + 1/(n+i)*((mu - addrow(i,:))'*(mu - addrow(i,:)));
mu = (n+i-1)/(n+i)*mu + 1/(n+i)*addrow(i,:);
end
upmu = mu;
upcovar = covar;
else option == 2
mu_min_j = n/(n-1)*(mu - 1/n*delrow);
upmu = mu - 1/n*data(delrow,:) + 1/n*addrow;
upcovar = covar - 1/n*((mu_min_j - data(delrow,:))'*(mu_min_j - data(delrow,:))) + 1/n*((mu_min_j - addrow)'*(mu_min_j - addrow))
end