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nisot:: geodesic_step is now based on RK4 instead of midpoint

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Zeno Rogue 2020-04-11 15:01:01 +02:00
parent 85443a14ab
commit c5d7479d00
1 changed files with 12 additions and 10 deletions
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22
nonisotropic.cpp
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@ -1970,18 +1970,20 @@ EX namespace nisot {
#endif
return true;
}
hyperpoint get_acceleration(const hyperpoint& at, const hyperpoint& vel) {
return christoffel(at, vel, vel);
}
EX void geodesic_step(hyperpoint& at, hyperpoint& velocity) {
auto acc = christoffel(at, velocity, velocity);
EX void geodesic_step(hyperpoint& at, hyperpoint& vel) {
/* RK4 method */
auto acc1 = get_acceleration(at, vel);
auto acc2 = get_acceleration(at + vel/2, vel + acc1/2);
auto acc3 = get_acceleration(at + vel/2 + acc1/4, vel + acc2/2);
auto acc4 = get_acceleration(at + vel + acc2/2, vel + acc3);
auto at2 = at + velocity / 2;
auto velocity2 = velocity + acc / 2;
auto acc2 = christoffel(at2, velocity2, velocity2);
at = at + velocity + acc2 / 2;
velocity = velocity + acc;
at += vel + (acc1+acc2+acc3)/6;
vel += (acc1+2*acc2+2*acc3+acc4)/6;
}
EX hyperpoint numerical_exp(hyperpoint v, int steps) {