Added script for RMSE on numerical forces

examples/snap/fnum.py

@@ -0,0 +1,24 @@
+import lammps
+
+def sqerr(a,b):
+    return (a[0]-b[0])**2+(a[1]-b[1])**2+(a[2]-b[2])**2
+
+infile = "in.fnum"
+
+fdeltalist = [1.0e-2,1.0e-3,1.0e-4,1.0e-5,1.0e-6,1.0e-7,1.0e-8,1.0e-9,1.0e-10]
+
+print("Fdelta RMSE")
+for fdelta in fdeltalist:
+    cmdlist = ["-screen","none","-var","fdelta",f'{fdelta}']
+    lmp = lammps.lammps(cmdargs = cmdlist)
+    lmp.file(infile)
+    natoms = lmp.get_natoms()
+
+    f = lmp.extract_atom("f")
+    fnum = lmp.extract_fix("fnum", lammps.LMP_STYLE_ATOM, lammps.LMP_TYPE_ARRAY)
+
+    sumsq = 0
+    for i in range(natoms):
+        sumsq += sqerr(fnum[i],f[i])
+    rmse = (sumsq/natoms)**0.5
+    print(f"{fdelta} {rmse}")