If <code>this</code> is an arbitrary perspective projection matrix obtained via one of the {@link #frustum(double, double, double, double, double, double) frustum()} methods
or via {@link #setFrustum(double, double, double, double, double, double) setFrustum()},
then this method builds the inverse of <code>this</code>.
<p>
This method can be used to quickly obtain the inverse of a perspective projection matrix.
<p>
If this matrix represents a symmetric perspective frustum transformation, as obtained via {@link #perspective(double, double, double, double) perspective()}, then
{@link #invertPerspective()} should be used instead.
If <code>this</code> is an arbitrary perspective projection matrix obtained via one of the {@link #frustum(double, double, double, double, double, double) frustum()} methods or via {@link #setFrustum(double, double, double, double, double, double) setFrustum()}, then this method builds the inverse of <code>this</code>. <p> This method can be used to quickly obtain the inverse of a perspective projection matrix. <p> If this matrix represents a symmetric perspective frustum transformation, as obtained via {@link #perspective(double, double, double, double) perspective()}, then {@link #invertPerspective()} should be used instead.
@see #frustum(double, double, double, double, double, double) @see #invertPerspective()
@return this