COMBINE CODE

        [BUNDLES\]COMBINE OutCube CODE In1 In2 [Off] [/FACTOR A1 A2]
      [/THRESHOLD T1 T2] [/BLANKING Bval]

      CODE is the operation code. Allowed values are
    ADD      or PLUS    OutCube = A1*In1 + A2*In2 + Off
    SUBTRACT or MINUS   OutCube = A1*In1 - A2*In2 + Off
    DIVIDE   or OVER    OutCube = A1*In1 / A2*In2 + Off
    MULTIPLY or TIMES   OutCube = A1*In1 * A2*In2 + Off
    OPACITY             OutCube = -Log( A1*In1 / A2*In2 + Off)
    INDEX               OutCube = Log( A1*In1 / A2*In2) / Log(Nu1/Nu2)
    where  Nu1  is  the  Frequency of In1, and Nu2 that of In2.  Off is 0 if not
    specified.