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With this setting, the 3rd derivatives in the curve points P[2] and P[n-1] are continuously forced, so that the acceleration profile from P[1] via P[2] to P[3] and from P[n-2] via P[n-1] to P[n] continues in the same way. As a result, the curve points P[2] and P[n-1] are no longer perceived as nodes because the acceleration profile does not bend at these points. However, this results in different speeds at the margins.