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backwardeuler.go
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/
backwardeuler.go
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package engine
import (
"github.com/mumax/3/cuda"
"github.com/mumax/3/data"
"github.com/mumax/3/util"
)
// Implicit midpoint solver.
type BackwardEuler struct {
dy1 *data.Slice
}
// Euler method, can be used as solver.Step.
func (s *BackwardEuler) Step() {
util.AssertMsg(MaxErr > 0, "Backward euler solver requires MaxErr > 0")
t0 := Time
y := M.Buffer()
y0 := cuda.Buffer(VECTOR, y.Size())
defer cuda.Recycle(y0)
data.Copy(y0, y)
dy0 := cuda.Buffer(VECTOR, y.Size())
defer cuda.Recycle(dy0)
if s.dy1 == nil {
s.dy1 = cuda.Buffer(VECTOR, y.Size())
}
dy1 := s.dy1
Dt_si = FixDt
dt := float32(Dt_si * GammaLL)
util.AssertMsg(dt > 0, "Backward Euler solver requires fixed time step > 0")
// Fist guess
Time = t0 + 0.5*Dt_si // 0.5 dt makes it implicit midpoint method
// with temperature, previous torque cannot be used as predictor
if Temp.isZero() {
cuda.Madd2(y, y0, dy1, 1, dt) // predictor euler step with previous torque
M.normalize()
}
torqueFn(dy0)
cuda.Madd2(y, y0, dy0, 1, dt) // y = y0 + dt * dy
M.normalize()
// One iteration
torqueFn(dy1)
cuda.Madd2(y, y0, dy1, 1, dt) // y = y0 + dt * dy1
M.normalize()
Time = t0 + Dt_si
err := cuda.MaxVecDiff(dy0, dy1) * float64(dt)
NSteps++
setLastErr(err)
setMaxTorque(dy1)
}
func (s *BackwardEuler) Free() {
s.dy1.Free()
s.dy1 = nil
}