If <code>this</code> is a perspective projection matrix obtained via one of the {@link #perspective(double, double, double, double) perspective()} methods
or via {@link #setPerspective(double, double, double, double) setPerspective()}, that is, if <code>this</code> is a symmetrical perspective frustum transformation,
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 when being obtained via {@link #perspective(double, double, double, double) perspective()}.
If <code>this</code> is a perspective projection matrix obtained via one of the {@link #perspective(double, double, double, double) perspective()} methods or via {@link #setPerspective(double, double, double, double) setPerspective()}, that is, if <code>this</code> is a symmetrical perspective frustum transformation, 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 when being obtained via {@link #perspective(double, double, double, double) perspective()}.
@see #perspective(double, double, double, double)
@return this