...

function [Ix_angle,Iy_angle,Ixy_angle]= ...
         inertang(Angle,Ix,Iy,Ixy)
%
% [Ix_angle,Iy_angle,Ixy_angle]= ...
%   inertang(Angle,Ix,Iy,Ixy)
% ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
% This function calculates the inertia 
% values for a geometry rotated by
% angle Angle.
%
% Angle     - angle to determine the inertia
%             values for in degrees.
%             (positive measured CCW from 
%             positive x-axis)
% Ix        - inertia about y-axis
% Iy        - inertia about x-axis
% Ixy       - product of inertia about x-y
%
% Ix_angle  - Ix at Angle
% Iy_angle  - Iy at Angle
% Ixy_angle - Ixy at Angle
%
% User m functions called:  none
%----------------------------------------------

degrad=pi/180; 
angle_rad=degrad*Angle; t2=2*angle_rad;
Iavg=0.5*(Ix+Iy); Idiff=0.5*(Ix-Iy);
cost2=cos(t2); sint2=sin(t2);
Ix_angle=Iavg+Idiff*cost2-Ixy*sint2;
Iy_angle=Iavg-Idiff*cost2+Ixy*sint2;
Ixy_angle=Idiff*sint2+Ixy*cost2;