FUNCTION: THM_EFI_DERIVE_EZ, E, B, minBz=minBz, minRat=minRat, ratio=ratio PURPOSE: DERIVES EZ ASSUMING EdotB = 0 INPUT: E - REQUIRED. Data structure in DSL B - REQUIRED. Data structure in DSL KEYWORDS: minBz - OPTIONAL. Keeps from divide by zero. DEFAULT = 0.01 nT minRat - OPTIONAL. Minimum value of Bz/|B|. DEFAULT = 0.1 ratio - OUTPUT. = Bz/|B| CALLING: thm_efi_derive_Ez, Edsl, Bdsl OUTPUT: Tplot INITIAL VERSION: REE 08-11-04 MODIFICATION HISTORY: REE 09_05_01 LASP, CU