dercol = Cells(1, Cells.Columns.Count).End(xlToLeft).Column
Range("U4:" & "cells(4,dercol" )_
.FormulaR1C1 = "=IF(RC[-1]="""","""",IF(ISNA(VLOOKUP(RC20,Tableau,MATCH(Feuil1!R1C,IrisSct,0)+2,FALSE)),""0"",IF(VLOOKUP(RC20,Tableau,MATCH(Feuil1!R1C,IrisSct,0)+2,FALSE)=""-"",0,VLOOKUP(RC20,Tableau,MATCH(Feuil1!R1C,IrisSct,0)+2,FALSE))))"