Merge pull request #334 from mumax/bugfix/MFM_Nz

Allow Nz=2,3,4,5 for MFM images

mag/mfmkernel.go

@@ -3,11 +3,12 @@ package mag
 import (
 	"bufio"
 	"fmt"
+	"math"
+	"os"
+
 	d "github.com/mumax/3/data"
 	"github.com/mumax/3/oommf"
 	"github.com/mumax/3/util"
-	"math"
-	"os"
 )
 
 func MFMKernel(mesh *d.Mesh, lift, tipsize float64, cacheDir string) (kernel [3]*d.Slice) {
@@ -105,10 +106,10 @@ func CalcMFMKernel(mesh *d.Mesh, lift, tipsize float64) (kernel [3]*d.Slice) {
 	{
 		util.Assert(size[Z] >= 1 && size[Y] >= 2 && size[X] >= 2)
 		util.Assert(cellsize[X] > 0 && cellsize[Y] > 0 && cellsize[Z] > 0)
-		util.AssertMsg(size[X]%2 == 0 && size[Y]%2 == 0, "Even kernel size needed")
-		if size[Z] > 1 {
-			util.AssertMsg(size[Z]%2 == 0, "Even kernel size needed")
-		}
+		// util.AssertMsg(size[X]%2 == 0 && size[Y]%2 == 0, "Even kernel size needed")
+		// if size[Z] > 1 {
+		// util.AssertMsg(size[Z]%2 == 0, "Even kernel size needed")
+		// }
 	}
 
 	// Allocate only upper diagonal part. The rest is symmetric due to reciprocity.

test/mfm_sizes.mx3

@@ -0,0 +1,27 @@
+/*
+	Checks if MFM images can be saved for all thicknesses with and without PBC.
+	There was once a bug (#93) where Nz=2,3,4,5 could not generate an MFM image.
+*/
+
+Nx := 63
+Ny := 64
+c := 4e-9
+
+Msat = 1 / mu0
+Aex = 10e-12
+
+for Nz := 1; Nz < 12; Nz++ {
+	SetGridSize(Nx, Ny, Nz)
+	SetCellSize(c, c, c)
+	SetGeom(Zrange(-NZ*c/2, c/2).Intersect(Circle(Nx * c).Add(Xrange(-c*Nx/4, c*Nx/4))))
+	m = vortex(1, 1)
+	SetPBC(0, 0, 0)
+
+	SaveAs(m, sprintf("m_%d.ovf", Nz))
+
+	MFMLift = 40e-9 // forces the calculation of the MFM kernel.
+	SnapshotAs(MFM, sprintf("MFM_%d.jpg", Nz))
+	SetPBC(2, 2, 0)
+	MFMLift = 40e-9 // forces the calculation of the MFM kernel.
+	SnapshotAs(MFM, sprintf("MFM_%d_PBC.jpg", Nz))
+}