symbols in subscript unrecognized?

[Daniel Müller <mueller@xxxxxxxxxxxxxxxx>]

Hi ferret users

Here is another thing i don't quite understand. I have a script which
gets some parameters (i.e. names of variables) and defines some symbols
for those. It then calls a subscript and hands some parameters to this
one. Now look at the following script(s) and the error it produces:

   go calc_correlation_map ($var_reg) PC_reg
    !-> go calc_correlation_map rvar PC_reg
   !
---------------------------------------------------------------------------
   ! Description: calculates correlation map based of ERA data & indexes

   ! arguments  : $1 : variable name            [MSL]
   !            : $2 : correlation type         [point, NAO, SOI,
NAO_JONES,
   !                                             NAO_NCEP, 
NAO_NCEP_DJFM
   !                                             PminEpoint,SminEpoint
   !                                             PminEwGL, SminEwGL,
   !                                             SH_AOI, PC_reg         
]
   !            : $3 : longitude
   !            : $4 : latitude
   !            : $5 : lag                      [0.]
   !            : $6 : file name
   !
   !
--------------------------------------------------------------------------------
 
   define symbol var_cc = $1%MSL%          ! Processed Variable to
correlate to
    !-> define symbol var_cc = rvar                ! Processed Variable
to correlate to
   define symbol type = $2%point%          ! Type of regression
    !-> define symbol type = PC_reg                ! Type of regression
   define symbol lon = $3%20w%             ! longitude for point
regression
    !-> define symbol lon = 20w            ! longitude for point
regression
   define symbol lat = $4%60N%             ! latitude for point
regression
    !-> define symbol lat = 60N            ! latitude for point
regression
   define symbol lag = $5%0%               ! lag
    !-> define symbol lag = 0              ! lag
   define symbol file_name = $6%file%      ! file (regridding for
NAO_NCEP only)
    !-> define symbol file_name = file     ! file (regridding for
NAO_NCEP only)
    
 
   ! -------------------------------------------------------------------
   ! calculate normalized variable
     go calc_normal_var ($var_cc)
    !-> go calc_normal_var rvar
   !
---------------------------------------------------------------------------
   ! Description: calculate normalized variable var
   !
   ! Comment    : this script uses a number of working variable
($var)_dummy
   !              1) Use an expilicit region for the calculation.
   !              2) File must be set befor running the script
   !
   ! Output     : Var_norm       ->  normalized variable var
   !            : Var_std        ->  standard deviation of variable var
   !
   ! author     : ChA  08/97 [christof@climate.unibe.ch]
   ! adapted by : DM 09/1999 [mueller@climate.unibe.ch]
   !
   ! Usage      : GO calc_normal_var varibale_name
   !
   ! arguments  : $1 : variable name            [MSL]
   !
   !
---------------------------------------------------------------------------
   !cancel mode verify
   ! - define symbol var
   define symbol var = $1%MSL%
     !-> define symbol var = rvar
    
   show grid ($var)
    !-> show grid rvar
    **ERROR: invalid command: grid for rvar is not available.
             (LOAD this variable and try SHOW GRID again.)
   show grid rvar
   Command file, command group, or REPEAT execution aborted
   yes? show grid ($var)
    !-> show grid rvar
       GRID GIC1
    name       axis              # pts   start                end
    LONGITUDE LONGITUDE          144mr   0E                   2.5W
    LATITUDE  LATITUDE            29 r   20N                  90N
    normal    Z
    TIME1     T (MON)            472 r   23485                23956
   yes? 
   

So it seems, that the command show grid ($var) does work when back in
ferret typed in manually, but doesn't in the subscript.
I invoke the show grid command, because the following command in my
script, 
   define symbol min_L = `($var),RETURN=LSTART`
causes ferret tho hang for several minutes and then to terminate itself
without any further error massage.

The variable rvar is defined as follows: 
   define symbol fn=pres.mon.mean.jan1958_apr1997.des.20_90
   define symbol klimavar=pres_des
   ...
   use "/usr/users/mueller/dataset/mout/($fn).data.cdf"
   let rvar=($klimavar)[d=2]


which seems to be correct, because the following datasets are open:

   yes? show data
        currently SET data sets:
       1>
/usr/users/mueller/dataset/Wallace/AO_index_jan1958_apr1997.cdf
    name     title                             I         J        
K         L
    AOI      AO Index                         ...       ...      
...       1:472
    
       2>
/usr/users/mueller/dataset/mout/pres.mon.mean.jan1958_apr1997.des.20_90.data.cdf
    name     title                             I         J        
K         L
    PRES_DES SLP_DESEASONED                   1:144     1:29     
...       1:472
    TREND_STEIG                               1:144     1:29     
...       ...
    TREND_ABSN                                1:144     1:29     
...       ...
    PRES_DES_MEAN                             1:144     1:29     
...       ...
    
       3>
/usr/users/mueller/dataset/ncep/pres.mon.mean.jan1958_apr1997.cdf
    name     title                             I         J        
K         L
    PRES     Monthly mean surface pressure    1:144     1:73     
...       1:472
    
       4>
/usr/users/mueller/dataset/mout/weight_my/pres.mon.mean.jan1958_apr1997.des.20_90.DeTrend.DeMean.cdf       
(default)
    name     title                             I         J        
K         L
    EXPVAR   Explained Variance               ...       ...      
1:472     ...
    DEXPVAR  Error  Explained Variance        ...       ...      
1:472     ...
    EOF                                       1:144     1:29     
1:472     ...
    PC                                        ...       ...      
1:472     1:472
    PRES_DES_CALC                                1:144     1:29     
...       1:472
 
   yes? 


Is there anybody who can tell me what's happening (or why it isn't)? And
even more: Does anybody know a workaround for this?

Thank you in advance!

Daniel