[freeflow] further cleanup convergence script.

test/freeflow/navierstokes/convergence.sh

 #! /bin/bash
+# usage: build the executable in the build directory, copy the file to the folder with the executable, an example command to run the script is ./convergence.sh test_ff_stokes_donea ./params.input 2 4
 
 if [ $# -ne 4 ]; then
   echo "usage: $0 EXECUTABLE_NAME PARAMS DIMENSION NUM_REFINEMENT_STEPS"
@@ -27,7 +28,7 @@ MAXCELLS=$INITIALCELLS
 for (( i=0; i <= $MAX; ++i )); do
   printf "refinement $i / $MAX "
   ((MAXCELLS *=2))
-  ./$1 params.input -Grid.Cells "$GRIDCELLS" -Grid.Refinement $i -Problem.PrintL2Error true &>> $LOGFILE
+  ./$1 $2 -Grid.Cells "$GRIDCELLS" -Grid.Refinement $i -Problem.PrintL2Error true &>> $LOGFILE
   echo "done."
 done
 
@@ -37,13 +38,15 @@ set terminal pngcairo size 1000,750
 set output 'convergence.png'
 set xrange [($INITIALCELLS-1):$MAXCELLS]
 set yrange [:1]
+set format x '10^{%L}'
+set format y '10^{%L}'
 set xlabel 'number of cells per dimension'
-set ylabel 'l2 error (abs)'
+set ylabel 'abs(l2 error)'
 set log x
 set log y" > $1.gp
 
-PLOT="plot x**-1 w l lc rgb 'gray40' t 'O_1', \
-x**-2 w l lc rgb 'blue20' t 'O_2', \
+PLOT="plot x**-1 w l lc rgb 'gray40' t 'order_1', \
+x**-2 w l lc rgb 'blue20' t 'order_2', \
 '$L2ERRORFILE' u (\$6**(1./$DIM.)):17 w lp t 'pressure', \
 '$L2ERRORFILE' u (\$6**(1./$DIM.)):23 w lp t 'velocity_x'"
 if [ $DIM == 2 ]; then