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temperature.go
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temperature.go
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package engine
import (
"github.com/mumax/3/cuda"
"github.com/mumax/3/cuda/curand"
"github.com/mumax/3/data"
"github.com/mumax/3/mag"
"github.com/mumax/3/util"
)
var (
Temp ScalarParam // Temperature in K
temp_red derivedParam // reduced temperature = (alpha * Temp) / (mu0 * Msat)
E_therm *GetScalar // Thermal energy in J
Edens_therm sAdder // Thermal energy density
B_therm thermField // Thermal effective field (T)
)
// thermField calculates and caches thermal noise.
type thermField struct {
seed int64 // seed for generator
generator curand.Generator //
noise *data.Slice // noise buffer
step int // solver step corresponding to noise
dt float64 // solver timestep corresponding to noise
}
func init() {
Temp.init("Temp", "K", "Temperature", []derived{&temp_red})
DeclFunc("ThermSeed", ThermSeed, "Set a random seed for thermal noise")
E_therm = NewGetScalar("E_therm", "J", "Thermal energy", GetThermalEnergy)
Edens_therm.init("Edens_therm", "J/m3", "Thermal energy density", makeEdensAdder(&B_therm, -1))
registerEnergy(GetThermalEnergy, Edens_therm.AddTo)
B_therm.step = -1 // invalidate noise cache
DeclROnly("B_therm", &B_therm, "Thermal field (T)")
// reduced temperature = (alpha * T) / (mu0 * Msat)
temp_red.init(1, []updater{&Alpha, &Temp, &Msat}, func(p *derivedParam) {
dst := temp_red.cpu_buf
alpha := Alpha.cpuLUT()
T := Temp.cpuLUT()
Ms := Msat.cpuLUT()
for i := 0; i < NREGION; i++ { // not regions.MaxReg!
dst[0][i] = safediv(alpha[0][i]*T[0][i], mag.Mu0*Ms[0][i])
}
})
}
func (b *thermField) AddTo(dst *data.Slice) {
if !Temp.isZero() {
b.update()
cuda.Madd2(dst, dst, b.noise, 1, 1)
}
}
func (b *thermField) update() {
// we need to fix the time step here because solver will not yet have done it before the first step.
// FixDt as an lvalue that sets Dt_si on change might be cleaner.
if FixDt != 0 {
Dt_si = FixDt
}
if b.generator == 0 {
b.generator = curand.CreateGenerator(curand.PSEUDO_DEFAULT)
b.generator.SetSeed(b.seed)
}
if b.noise == nil {
b.noise = cuda.NewSlice(b.NComp(), b.Mesh().Size())
// when noise was (re-)allocated it's invalid for sure.
B_therm.step = -1
B_therm.dt = -1
}
if Temp.isZero() {
cuda.Memset(b.noise, 0, 0, 0)
b.step = NSteps
b.dt = Dt_si
return
}
// Finite temperature cannot work with RK23 solver because of FSAL property:
// last torque is re-used for next step, but then the field has jumped
// so the previous torque is not valid anymore.
// Also, as the amplitude of the thermal field depends on dt, we require dt
// to be fixed. Otherwise some hard-to-grasp feedback loop with the adaptive
// time step would occur.
//TODO
util.AssertMsg(((solvertype != BOGAKISHAMPINE) && (solvertype != DORMANDPRINCE)), "Temperature requires Euler, Heun or Runge Kutta4 solver type")
util.AssertMsg(FixDt != 0, "Temperature requires fixed time step")
// keep constant during time step
if NSteps == b.step && Dt_si == b.dt {
return
}
N := Mesh().NCell()
k2mu0_VgammaDt := 2 * mag.Mu0 * mag.Kb / (GammaLL * cellVolume() * Dt_si)
noise := cuda.Buffer(1, Mesh().Size())
defer cuda.Recycle(noise)
const mean = 0
const stddev = 1
dst := b.noise
for i := 0; i < 3; i++ {
b.generator.GenerateNormal(uintptr(noise.DevPtr(0)), int64(N), mean, stddev)
cuda.SetTemperature(dst.Comp(i), noise, temp_red.gpuLUT1(), k2mu0_VgammaDt, regions.Gpu())
}
b.step = NSteps
b.dt = Dt_si
}
func GetThermalEnergy() float64 {
if Temp.isZero() || relaxing {
return 0
} else {
return -cellVolume() * dot(&M_full, &B_therm)
}
}
// Seeds the thermal noise generator
func ThermSeed(seed int) {
B_therm.seed = int64(seed)
if B_therm.generator != 0 {
B_therm.generator.SetSeed(B_therm.seed)
}
}
func (b *thermField) Mesh() *data.Mesh { return Mesh() }
func (b *thermField) NComp() int { return 3 }
func (b *thermField) Name() string { return "Thermal field" }
func (b *thermField) Unit() string { return "T" }
func (b *thermField) average() []float64 { return qAverageUniverse(b) }
func (b *thermField) Slice() (*data.Slice, bool) {
b.update()
return b.noise, false
}