The planar simple pendulum is composed by a lumped mass of 1 kg and
a massless link of 1 m length.
The system is under gravity effects (9.81 N/kg acting in the negative *y* direction).
The position of the global reference frame is shown in the figure.

The analysis to be performed is a dynamic simulation with a duration of 2000 s.
Initially, the system is at rest (all velocities are zero) and in horizontal position:
the value for the *x*-coordinate of point P1 is +1.0 m.

The reference solution for this problem is the time-history of the position of point P1 (*x* and *y* coordinates). The maximun allowed errors are 1.0E-1 (low precission) and 1.0E-3 (high precission), measured with 4000 output steps and a threshold value of 1.0E-3.

The following information is provided:

- Time-history of the position of point P1, as text data file: A01_solution_data.txt
- Animation of the system, as AVI movie: (first 5 s) A01_solution_movie.avi
- Time-history of the position of point P1, as plot (first 10 s):