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Incorrect HK4 #10

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zoharl3 opened this issue Jul 21, 2022 · 0 comments
Open

Incorrect HK4 #10

zoharl3 opened this issue Jul 21, 2022 · 0 comments

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@zoharl3
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zoharl3 commented Jul 21, 2022

I believe you are missing the first term:

https://en.wikipedia.org/wiki/Runge%E2%80%93Kutta_methods

https://www.geeksforgeeks.org/runge-kutta-4th-order-method-solve-differential-equation/

Specifically, update integrator.h, integratePointSet() to

else if (mode == IntRK4) {
        PosType x0(x);
        std::vector<Vec3> uTotal(u);
        
        for(int i=0; i<N; i++) {
            x[i].pos = x0[i].pos + 0.5*u[i];
            uTotal[i] += u[i]; // zl was missing?
        }

The change in result doesn't seem significant, but still.
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