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   Computes inertias of common objects about their c.m. All objects
   have their axis of symmetry about z. If you enter a thickness with
   'cylinder', 'box' or 'sphere' it will automatically compute the hollow
   versions. The output is in the form:
   [ixx iyy izz ixy ixz iyz] unless four arguments are entered, in which
   case it outputs a 3x3 matrix.
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   Form:
   inr = Inertias( m, x, type, matType )
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   ------
   Inputs
   ------
   m 		      (1,1) Mass
   x 		            Relevant dimensions
   type                Type of solid
                       'sphere'          x = [radius]
                       'box'             x = [xLength, yLength, zLength]
                       'plate'           x = [xLength, yLength]
												'disk'						x = [radius]
                       'cylinder'        x = [radius, zLength] 
                       'ellipsoid'       x = [a b c]
                       'hollow cylinder' x = [radius, zLength, thickness]
                       'hollow box'      x = [xLength, yLength, zLength, thickness]
                       'hollow sphere'   x = [radius, thickness]
   matType       (1,1) Any argument causes the routine to return a 3x3 matrix

   -------
   Outputs
   -------
   inr     (1,6)   Inertia matrix

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