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Hi Robert, When multiple grid files are used, a + character is used in the GDFILE variable to separate the filenames. When referencing which file a grid field should be found, the variable is appended with +n, where n is the number of the grid file in the order given in GDFILE. For your example try GFUNC = sub(p03m^110201/0600F015,p03m+2^110201/1200F012) Michael James Unidata > Support: > > I am trying to plot 3-hour precipitation from wrf model gridded output by > subtracting total precipitation from consecutive 3-hour gempak files named > wrfprs_d01.012.grd and wrfprs_d01.015.grd. > > The map plots but without precip contours. My gdplot list is as follows: > > *********************************************************************************************** > GDFILE Grid file wrfprs_d01.012.grd + > wrfprs_d01.015.grd > GDATTIM Grid date/time f015 > GLEVEL Grid level 0 > GVCORD Grid vertical coordinate none > PANEL Panel loc/color/dash/width/regn 0 > SKIP Skip_cntr/skip_plt_x;skip_plt_y /2;2 > SCALE Scalar scale / vector scale 0 > GFUNC Scalar grid > sub(p03m^110104/1200F015,p03m^110104/1200F012) > CTYPE Contour type: C/F c > CONTUR Subbox/smooth 1/1 > CINT Contour interval/min/max .5/0/20 > LINE Color/type/width/label/smth/fltr 1/1/1/1 > FINT Fill interval/min/max > FLINE Fill colors/fill types > HILO Color/symbol/rng/rad/cnt/intp > HLSYM HILO txt size/posn/font/wdth/hw > CLRBAR Color/ornt/anch/x;y/ln;wd/freq|t > GVECT Vector grid > WIND Wind symbol/siz/wdth/typ/hdsz brbk3 > REFVEC Mag;x;y;txtsiz/font/wdth/HW;labl > TITLE Title color/line/title > TEXT Size/fnt/wdth/brdr/N-rot/just/hw .85/2/hw > CLEAR Clear screen flag yes > GAREA Graphics area dset > IJSKIP Iskp;Istrt;Istp/Jskp;Jstrt;Jstp > PROJ Map projection/angles/margins|dr lcc > MAP Map color/dash/width/filter flag > MSCALE fgc;bgc;mask/units/lat;hide/valu > LATLON Line color/dash/width/freq/inc/l > DEVICE Device|name|x size;y size|color xw > STNPLT Txtc/txt attr|marker attr|stnfil > GEMPAK-GDPLOT>r > Creating process: xw for queue 294917 > [DG -7] Input grid P03M ^110104/1200F015 @0 %NONE in SUB cannot be found. > [GDPLOT 2] The requested scalar/vector cannot be computed. > ******************************************************************************************* > > Can you suggest a method to plot the time difference of scalar fields from > two gempak files? I tried using tdf instead of sub, but it doesn't work > either. > > Thanks, > > Bob Ballentine > > Ticket Details =================== Ticket ID: YIQ-950675 Department: Support GEMPAK Priority: Normal Status: Open