The motion of the mass1 is forced depending on the motion
of mass2. The dependency is given by a cubic polynomial.
This example demonstrates the meaning of the function evaluating
the 2nd derivative of a polynomial with respect to time.
Without this function, the DAE index reduction of the mechanical
system would fail since positionByPolynomial.s, which prescribes
the motion of mass1, needs to be differentiated twice.
In order to check proper differentiation, the block evalPolynomial3
is provided which only evaluates a cubic polynomial of the same
coefficients like positionByPolynomial.
The signal differences given by add block shall, thus, be zero
(see simulation results of add[1].y, add[2].y
and add[3].y).