function [STRESS,ALPHA] = ROTATESTRESS(L,S,A)
%******************************************************************************
% Rotate stress and back stress to the mid-configuration L = [dui/dxj]        %
%******************************************************************************
%%                                                                            %
 STR=[S(1) S(4) S(6);S(4) S(2) S(5);S(6) S(5) S(3)];            % Stress matrix
 ALP=[A(1) A(4) A(6);A(4) A(2) A(5);A(6) A(5) A(3)];       % Back stress matrix
 R = L*inv(eye(3) - 0.5*L);                 % Displacement gradient at midpoint
 W = .5*(R-R');                                       % Spin tensor at midpoint
 R = eye(3) + inv(eye(3) - 0.5*W)*W;                 % Rotation to the midpoint
 STR = R*STR*R';                                                % Rotate stress
 ALP = R*ALP*R';                                           % Rotage back stress
 STRESS=[STR(1,1) STR(2,2) STR(3,3) STR(1,2) STR(2,3) STR(1,3)]';  % Voigt form
 ALPHA =[ALP(1,1) ALP(2,2) ALP(3,3) ALP(1,2) ALP(2,3) ALP(1,3)]';  % Voigt form
end                                                                           %