SUB correl(Ce(),Cm(),E,M,esave(),msave(),pass,nsave)
    ! accumulate data for time correlation functions
    ! save last nsave values of M and E
    ! index0 = array index for earliest saved time
    LET index0 = mod(pass-1,nsave) + 1
    IF pass > nsave then
       ! compute Ce and Cm after nsave values are saved
       LET index = index0
       FOR tdiff = nsave to 1 step -1
           LET Ce(tdiff) = Ce(tdiff) + E*esave(index)
           LET Cm(tdiff) = Cm(tdiff) + M*msave(index)
           LET index = index + 1
           IF index > nsave then LET index = 1
       NEXT tdiff
    END IF
    ! save latest value in array position of earliest value
    LET esave(index0) = E
    LET msave(index0) = M
END SUB