My newtfunc contain the varion and unknown solution,but the newton method in IDL just allow given initially solution of the equation. How to get the the Solution of the equation ?Thanks Pro TSM_lixiaModel ;http://www.harrisgeospati...deTileIterators.html !Except=0 Compile_opt idl2 e=Envi(/headless) starttime = Systime(/second) dir='I:\lwkDATA\waterRegion\MODIS\' files=file_search(dir,'*RC.tif',count=num) for i=0,num-1 do begin file=files[i] raster=e.Openraster(file,external_type='ADS40') outFile=file_dirname(file)+'\'+file_basename(file,'.tif')+'_TSM_lixiaModel.tif' TSMraster=enviraster(uri=outfile,$ nrows=raster.nrows,$ ncolumns=raster.ncolumns,$ nbands=1,$ data_type=raster.data_type,$ SPATIALREF=raster.SPATIALREF) tileIterator=raster.createtileiterator(bands=2,tile_size=[100,100]) count=0 foreach tile,tileiterator do begin count++ Rrs=prov(tile) ;Tile is variable, but not the needed Solution of the equation ;S is needed Solution of the equation processedTile=newton(??????,'newtfunc'); currentSubRect=tileIterator.Current_subrect TSMraster.setdata,processedTile,sub_rect=currentsubrect print,'1' endforeach TSMraster.save endfor End function newtfunc,S compile_opt idl2 return,(r-93.0943)*S+49.2464*S*exp(-0.0001*S)-344.016+45*r end