function [STR,ALP,EP,D]=COMBHARD(MP,D,DEPS,STRN,ALPN,EPN,LTAN)
%******************************************************************************
% Linear combined isotropic/kinamtic hardening plasticity model               %
%******************************************************************************
%%                                                                            %
 IDEN = [1 1 1 0 0 0]'; TWO3=2/3; STWO3=sqrt(TWO3);  % Identity tensor & const.
 MU=MP(2); BETA=MP(3); H=MP(4); Y0=MP(5);                 % Material properties
 STRTR=STRN + D*DEPS;                                            % Trial stress
 I1=sum(STRTR(1:3));                                           % Trace(sigmatr)
 STR=STRTR - I1*IDEN/3;                                     % Deviatoric stress
 ETA=STR - ALPN;                                               % Shifted stress
 ETAT=sqrt(ETA(1)^2+ETA(2)^2+ETA(3)^2+2*(ETA(4)^2+ETA(5)^2+ETA(6)^2));   % Norm
 FYLD=ETAT - STWO3*(Y0+(1-BETA)*H*EPN);                  % Trial yield function
 if FYLD<Y0*1E-6, STR=STRTR; ALP=ALPN; EP=EPN; return; end      % Elastic state
 GAMMA=FYLD/(2*MU + TWO3*H);                        % Plastic consistency param
 N=ETA/ETAT;                                          % Unit vector normal to f
 EP=EPN + GAMMA*STWO3;                            % Updated eff. plastic strain
 STR=STRTR - 2*MU*GAMMA*N;                                     % Updated stress
 ALP=ALPN + TWO3*BETA*H*GAMMA*N;                          % Updated back stress
 if LTAN                         % Algorithmic tangent stiffness for plasticity
  V1=4*MU^2/(2*MU+TWO3*H); V2=4*MU^2*GAMMA/ETAT;                 % Coefficients
  D=D - (V1-V2)*(N*N') + V2*(IDEN*IDEN')/3;                 % Tangent stiffness
  D(1,1)=D(1,1)-V2; D(2,2)=D(2,2)-V2; D(3,3)=D(3,3)-V2;      % From 4th-order I
  D(4,4)=D(4,4)-.5*V2; D(5,5)=D(5,5)-.5*V2; D(6,6)=D(6,6)-.5*V2;              %
 end                                          % End of tangent stiffness branch
end                                                                           %