Parallel bash for loop to lattices tutorial.

Former-commit-id: 065638f79fbe8f37f681dd10f93b9914883c9577

lattices.md

@@ -80,7 +80,16 @@ This pre-calculates the translation operators for a simple (one particle per uni
 621 nm × 571 nm rectangular lattice inside a medium with refractive index 1.52, 
 up to the octupole (`lMax` = 3) order, yielding one file per frequency. 
 This can take some time and
-it makes sense to run a parallelised `for`-loop instead.
+it makes sense to run a parallelised `for`-loop instead; this is a stupid but working
+way to do it in bash:
+```
+  N=4   # number of parallel processes
+  for omega in $(cat omegalist); do
+    ((i=i%N)); ((i++==0)) && wait
+    ew_gen_kin $omega 621e-9 0 0 571e-9 3 w_$omega 1.52 1 0 0 < klist
+    echo $omega   # optional, to follow progress
+  done
+```
 
 When this is done, we convert all the text output files into 
 numpy's binary format in order to speed up loading in the following steps.
@@ -94,7 +103,7 @@ is the destination path for the converted data (this will be
 a directory), and the remaining arguments are paths to the
 files generated by `ew_gen_kin`. In the case above, one could use
 ```
-  processWfiles_sortnames.py 1 all s_*
+  processWfiles_sortnames.py 1 all w_*
 ```
 which would create a directory named `all` containing several
 .npy files.