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Per Glenn Fiedler 'Integration Basics' (gafferongames.com), SEMI-IMPLICIT EULER (a.k.a. symplectic Euler) updates velocity and position in which order?
ASkip velocity update; recompute it from position diff
BUpdate position first, then use OLD velocity to update later
CUpdate velocity first, then use NEW velocity to update position
DUpdate both with the same old values of last frame
Answer & Solution
Correct answer: C. Update velocity first, then use NEW velocity to update position
Fiedler 'Integration Basics': v_{n+1} = v_n + a·dt; x_{n+1} = x_n + v_{n+1}·dt. Symplectic — conserves energy over long simulations vs explicit Euler.
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