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John, Your problem lies in your syntax. To produce the magnitude of the wind as you wrote: sqrt(avn_urel**2+avn_vrel**2) The GEMPAK syntax would be: sqrt(sum(mul(avn_urel,avn_urel),mul(avn_vrel,avn_vrel))) Luckily, this is more easily done by taking the magnitude of the constituted vector from avn_urel and avn_vrel: mag(vecr(avn_urel,avn_vrel)) Steve Chiswell >From: John Merrill <address@hidden> >Organization: UCAR/Unidata >Keywords: 200306131814.h5DIEbLd001292 >This is a multi-part message in MIME format. >--------------030700040704020404080503 >Content-Type: text/plain; charset=us-ascii; format=flowed >Content-Transfer-Encoding: 7bit > >Hello, > I'm using .gem files prepared from the Reanlaysis CD-ROM, monthly >average fields. The variable names differ from >the usual ones, of course, but I encounter a difficulty in calculating >even a simple scalar. At glevel=200 I want to plot >iostachs; the components of the wind here are avn_urel, avn_vrel (avn >for 'average,' I suppose). I tried to compute a new >quantity by setting gfunc=sqrt(avn_urel**2+avn_vrel**2)//avn_s, was >dismayed to get the response that "requested grid >avn_urel**2 in (specifications) cannot be found"; then, of course "The >requested scalar/vector cannot be computed." You'd >be correct assuming I've not defined/computed grids previously.... >Thanks. John > >--------------030700040704020404080503 >Content-Type: text/plain; x-mac-type="0"; x-mac-creator="0"; > name="200ZSrestore" >Content-Transfer-Encoding: 7bit >Content-Disposition: inline; > filename="200ZSrestore" > >! >! Restore File : 200 Height and Isotachs >! >! Log: >! J. Merrill 7/02 Initial creation as 500_msl composite >! J. Merrill 6/32 Revise for height/isotach only >! >garea 20;85;60;150 >LATLON 8/2/2//15;15 >MAP 8/1/2 >GVCORD= pres !pres >GLEVEL 200 !200 >SKIP 0 !0 >SCALE -1 !0 >gfunc avn_urel//urel !avn_vrel//vrel >gfunc hght !sped >TYPE c !c >CONTUR 2/2 !2/2 >CINT 6 !10 >LINE 32/1/3 !32/2/2 >TITLE 32/-1/~ 200 hPa Height and Isotachs, April 2001 Mean >TEXT 2/1/3/sw >border //3 >CLEAR yes > >--------------030700040704020404080503-- >