[gradsusr] error with area average scripts

[Sahidul]

Dear sir,
I want to plot the diurnal variation of the difference between 2 different
data files  averaged over a rectangular area. I am using following script.
It is showing error like

*Operation error:  Invalid dimension environment  Too many varying
dimensions*

==================
'reinit'
'clear'
'open rh_ncep1.ctl'
'open rh_ncep3.ctl'
'open rh_ncep3.ctl'

'set parea 2 10 1.8 7.5'
'set lat 22'
'set lon 85'
'set xlopts 1 6 0.19'
'set ylopts 1 6 0.19'
'set map 1 1 6'
'set t 13 36'
'set z 2 14'
'set display color white'
'set mpdset hires'
'set grads off'
'set grid off'
'set gxout shaded'
'set clevs -8 -6 -4 -2 0 2 4 6 8'
'd aave((rh.1-rh.3),lon=70,lon=100,lat=17,lat=25)'
'draw ylab height(km)'
'draw title diff RH(%) with height levels'
'print file.eps'
'!convert  file.eps ./ncep1_cep3.jpg'
'quit'
==================
Please help

-Sahidul
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://gradsusr.org/pipermail/gradsusr/attachments/20140824/dd80c681/attachment.html