%The function calculates the matrix for rotating the stress tensor around y-axis.
%Inputs:
    %alpha- rotation angle.
%Outputs:
    %N- the matrix used to rotate the stress tensor around y-axis.
function N=StrRMatrixY(alpha)
N=[cos(alpha) 0 -sin(alpha);
   0 1 0;
   sin(alpha) 0 cos(alpha)];