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Allows odd N mesh for nonzero Temp #401

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Allows odd N mesh for nonzero Temp #401

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2 changes: 2 additions & 0 deletions cuda/temperature.go
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,8 @@ import (
// Set Bth to thermal noise (Brown).
// see temperature2.cu
func SetTemperature(Bth, noise *data.Slice, k2mu0_Mu0VgammaDt float64, Msat, Temp, Alpha MSlice) {

// N is set by the length of Bth. noise is now set to length N+N%2 (N when N is even, N+1 when N is odd) in engine/temperature.go, so noise[N] is a dummy value that should never be used. The kernel only cares about the underlying pointer and the explicit N count, not the declared shape.
util.Argument(Bth.NComp() == 1 && noise.NComp() == 1)

N := Bth.Len()
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25 changes: 12 additions & 13 deletions engine/temperature.go
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Original file line number Diff line number Diff line change
@@ -1,15 +1,12 @@
package engine

import (
"fmt"

"math"

"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 (
Expand All @@ -20,7 +17,6 @@ var (
)

var AddThermalEnergyDensity = makeEdensAdder(&B_therm, -1)
var PrintedWarningTempOddGrid = false // Will be set to true if the warning about odd temperature has been printed already, to avoid spam.

// thermField calculates and caches thermal noise.
type thermField struct {
Expand Down Expand Up @@ -91,15 +87,18 @@ func (b *thermField) update() {
}

N := Mesh().NCell()
if !PrintedWarningTempOddGrid && N%2 > 0 { // T is nonzero if we have gotten this far. As noted in issue #314, this means the grid size must be even.
PrintedWarningTempOddGrid = true
warnStr := "// WARNING: nonzero temperature requires an even amount of grid cells,\n" +
"// but all axes have an odd number of cells: %v.\n" +
"// This may cause a CURAND_STATUS_LENGTH_NOT_MULTIPLE error." // Error is likely when the largest factor is >127
util.Log(fmt.Sprintf(warnStr, Mesh().Size()))
}

// CURAND's GenerateNormal uses Box-Muller, which requires an even length. If N is odd, we allocate
// one extra float so CURAND is satisfied. The settemperature2 kernel guards
// on i < N (derived from B's size, not noise's size), so noise[N] is written but never read.
Npad := int64(N + (N % 2))
k2_VgammaDt := 2 * mag.Kb / (GammaLL * cellVolume() * Dt_si)
noise := cuda.Buffer(1, Mesh().Size())

// Use the exact mesh shape when N is already even (common case, no overhead), equivalent to Mesh().Size()
// When N is odd, use a flat [Npad,1,1] shape — the Cuda kernel only cares about
// the underlying pointer and the explicit N count, not the declared shape.
noise := cuda.Buffer(1, [3]int{int(Npad), 1, 1})

defer cuda.Recycle(noise)

const mean = 0
Expand All @@ -112,7 +111,7 @@ func (b *thermField) update() {
alpha := Alpha.MSlice()
defer alpha.Recycle()
for i := 0; i < 3; i++ {
b.generator.GenerateNormal(uintptr(noise.DevPtr(0)), int64(N), mean, stddev)
b.generator.GenerateNormal(uintptr(noise.DevPtr(0)), Npad, mean, stddev)
cuda.SetTemperature(dst.Comp(i), noise, k2_VgammaDt, ms, temp, alpha)
}

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