[ferret_users] how to integrate within a mixed layer?

[yangxing zheng <yangxingz@xxxxxxxxx>]

Hi ferreters,

    I do have a question about how to integrate a
variable within a mixed layer. Suppose I have a
dataset with only one variable MLD, which store the
value of mixed layer depth. I have another dataset
with a variable HEAT, for example, which is heat
advection.

   How can I integrate heat within mixed layer depth?

   I did this way:

  set data heat.nc  ! dataset with variable HEAT
  set data mld.nc   ! dataset with variable MLD

   let beg = 0
   let end = mld[d=2]
   define symbol zz = `beg`:`end` ! attempt to define
the integral interval

   let heat_mld = heat[d=1,z=($zz)@din]

  ......


  However, it is wrong since ferret says: invalid
command: grave accent does not evaluate to scalar
mld[d=2]

   Can anyone here help me with this problem? By the
way, both datasets have the same horizontal grid.

   Thanks!

   Yangxing