[gradsusr] Problem calculating the difference between two files

[Arlindo Meque]

Dear all,

	1. I want to obtain the   difference between   the precipitation forecast  (1.875X1.25 resolution) and the observed rainfall (2.5X2.5 resolution).
	2. These are the commands  I am using :reinit'
'set display color white'
'c'
'sdfopen oo.nc'                     *observed
'sdfopen  ff.nc'                    * forecasted
'set dfile 1'
'set t 1 14'
'set z 1'
'set lon 10 55'
'set lat -35 -10'
'define obs=ave(prcp_est,t=1,t=14)'

'set dfile 2'
'set t 1 14'
'set z 1'
'set lon 10 55'
'set lat -35 -10'
'define gg=ave(precip*86400,t=1,t=14)'
'define forecast=re(gg,2.5,2.5,ba)'            * regridding  the forecast
'define difference=forecast-obs'
'd difference'

 
	1. But Iam getting the following error message:Data Request Error: Invalid grid coordinates
  World coordinates convert to non-integer  grid coordinates
    Variable = obs  Dimension = 3 
  Error ocurred at column 10
DEFINE error:  Invalid expression 

4. Help is needed


Arlindo
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