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demag.go
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demag.go
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package engine
// Calculation of magnetostatic field
import (
"github.com/mumax/3/cuda"
"github.com/mumax/3/data"
"github.com/mumax/3/mag"
)
// Demag variables
var (
Msat ScalarParam
Bsat derivedParam
M_full vSetter
B_demag vSetter
E_demag *GetScalar
Edens_demag sAdder
EnableDemag = true // enable/disable demag field
conv_ *cuda.DemagConvolution // does the heavy lifting and provides FFTM
DemagAccuracy = 6.0 // Demag accuracy (divide cubes in at most N^3 points)
CacheDir = "" // directory for kernel cache
)
func init() {
Msat.init("Msat", "A/m", "Saturation magnetization", []derived{&Bsat, &lex2, &ku1_red, &kc1_red, &temp_red})
M_full.init("m_full", "A/m", "Unnormalized magnetization", SetMFull)
DeclVar("EnableDemag", &EnableDemag, "Enables/disables demag (default=true)")
DeclVar("DemagAccuracy", &DemagAccuracy, "Controls accuracy of demag kernel")
B_demag.init("B_demag", "T", "Magnetostatic field", SetDemagField)
E_demag = NewGetScalar("E_demag", "J", "Magnetostatic energy", GetDemagEnergy)
Edens_demag.init("Edens_demag", "J/m3", "Magnetostatic energy density", addEdens(&B_demag, -0.5))
registerEnergy(GetDemagEnergy, Edens_demag.AddTo)
//Bsat = Msat * mu0
Bsat.init(SCALAR, []updater{&Msat}, func(p *derivedParam) {
Ms := Msat.cpuLUT()
for i, ms := range Ms[0] {
p.cpu_buf[0][i] = mag.Mu0 * ms
}
})
}
// Sets dst to the current demag field
func SetDemagField(dst *data.Slice) {
if EnableDemag {
demagConv().Exec(dst, M.Buffer(), geometry.Gpu(), Bsat.gpuLUT1(), regions.Gpu())
} else {
cuda.Zero(dst) // will ADD other terms to it
}
}
// Sets dst to the full (unnormalized) magnetization in A/m
func SetMFull(dst *data.Slice) {
// scale m by Msat...
msat, rM := Msat.Slice()
if rM {
defer cuda.Recycle(msat)
}
for c := 0; c < 3; c++ {
cuda.Mul(dst.Comp(c), M.Buffer().Comp(c), msat)
}
// ...and by cell volume if applicable
vol, rV := geometry.Slice()
if rV {
defer cuda.Recycle(vol)
}
if !vol.IsNil() {
for c := 0; c < 3; c++ {
cuda.Mul(dst.Comp(c), dst.Comp(c), vol)
}
}
}
// returns demag convolution, making sure it's initialized
func demagConv() *cuda.DemagConvolution {
if conv_ == nil {
SetBusy(true)
defer SetBusy(false)
kernel := mag.DemagKernel(Mesh().Size(), Mesh().PBC(), Mesh().CellSize(), DemagAccuracy, CacheDir)
conv_ = cuda.NewDemag(Mesh().Size(), Mesh().PBC(), kernel)
}
return conv_
}
// Returns the current demag energy in Joules.
func GetDemagEnergy() float64 {
return -0.5 * cellVolume() * dot(&M_full, &B_demag)
}