function R=f_decay_rk(t,c,flag,k)

%* R=f_decay(k, c) 
%
%  NOTE: for this to work in Matlab,  the parameter flag
%  must  be included before any passed parameters
% input:	k: decay constant
%		c: concentation at current time
% return:	R=decay rate this time step
R=-k*c;