!set pass=30
lambd=!mathsubst x=$centrex in $f
lambd=!evalsubst y=$centrey in $lambd


 !set minf=$lambd
!set maxf=$lambd
 !for a=-$pass to $pass
 !for b=-$pass to $pass
c=!mathsubst x=$[$centrex+($a)*$xy_size/$pass] in $f 
c=!evalsubst y=$[$centrey+($b)*$xy_size/$pass] in $c

!if $[abs($c)]<1000 
!set maxf=!evalue max($c,$maxf)
!set minf=!evalue  min($c,$minf)
!endif
!next b
!next a

!set nombre_niveau= 20
!set nstep= !evalue ($maxf-($minf))
!set p= !evalue $[rint((-$lambd+($minf))*$nombre_niveau/$nstep)]
!set q= !evalue $[rint((-$lambd+($maxf))*$nombre_niveau/$nstep)]



!set niveau=
!for i=$p to $q
r=!evalue $lambd+($i)*$nstep/$nombre_niveau
niveau=!append  item $r  to $niveau 
!next i


