DATE     94/01/10
     Opérateur BASE
     --------------

     Cas 1 :
     -----
     BAS1 = BASE  STRU1 (ATTA1) (SOL1) (SOL2)  ;

     Cas 2 :
     -----
     TAB1 = BASE  TAB2  TAB3  | 'PLUS'   VEC1   ;
                              | 'ROTA'   FLOT1  P1  P2  ;

     Description :
     ------------

     1st case :
     ---------
     In a modal base analysis, a structure is represented
 by a set of modes and static solutions.
 The specification of the linkages which act on the
 structure as well as that of the set of modes and static
 solutions define the problem to be solved.
 The BASE operator enables the user to construct an object
 (BASEMODA type) which includes all this information.
 

     2nd case  :
     ----------
     The BASE operator carries out a geometric operation of 
 translation ('PLUS') or rotation ('ROTA') on an object 
 containing modes and pseudo-modes of a structure.
 

    Contents :
    ___________

    STRU1   : object containing the structure description, either
              elementary, or composed of identical substructures.
              (STRUCTUR type)

    ATTA1   : object containing the specification of the linkages 
              (ATTACHE type)

    SOL1    : object containing the set of modes
              (SOLUTION type, MODE subtype)

    SOL2    : object containing the set of static solutions
              (SOLUTION type, SOLUTION STATIQUE subtype)

    The specification of modes, linkages, and static solutions 
 is optional.

    TAB1    : object containing the structure modal characteristics 
              after translation or rotation (TABLE type).
              TAB1 structure :   TAB1.'BASE'  = TAB4
                                     .'POINT' = TAB5
                TAB4 has the same structure as TAB2.
                TAB5 provides the correspondence between the points 
                     contained in TAB3 (TABLE type) in the new
                     geometry.
                     TAB5.(TAB3.I) = QI , QI is the point which
                     corresponds, at the level of the modified
                     geometry, to the point PI = TAB3.I of the
                     initial geometry

    TAB2    : object containing the initial structure modal 
              characteristics (TABLE type),
              BASE_MODALE subtype table

    TAB3    : TABLE type object indexed by INTEGERs varying from
              1 to N and containing points of the geometry, POINT 
              subtype table 
              
    'PLUS'  : MOT type object indicating that the geometrical 
              operation carried out is a translation of vector VEC1 
              (POINT type object)
              
    'ROTA'  : MOT type object indicating that the geometrical
              operation carried out is a rotation of angle FLOT1 
              (in degrees) about the axis defined by the point P1
              (in 2D) or the points P1 and P2 (in 3D)
             


    Possible combinations :
    _______________________

    If STRU1 is elementary :

      BAS1 = BASE  STRU1 ATTA1 SOL1 SOL2 ;
      BAS2 = BASE  STRU1 ATTA1 SOL1      ;
      BAS3 = BASE  STRU1 ATTA1      SOL2 ;
      BAS4 = BASE  STRU1 ATTA1           ;
      BAS5 = BASE  STRU1       SOL1      ;

    If STRU is a set of identical substructures :

      BAS6 = BASE  STRU1 ATTA1 SOL1     ;
      BAS7 = BASE  STRU1 ATTA1          ;
      BAS8 = BASE  STRU1       SOL1     ;

    Note :
    ________

    If the static solutions are infered from the linkages, the 
 BASE operator calculates automatically the static solutions by
 default.

    Reading of an elementary base :
    _______________________________

    Operators such as PJBA, EVOL, RECO,... require an elementary
 base, i.e. a modal base different from a set of sub-bases, as 
 operands.

    There are three reading possibilities :

      BAS         : read the elementary base BAS
      BAS STRU    : read the elementary base taken from BAS,
                    associated with the substucture STRU 
      BAS STRU N1 : search for the elementary base BAS, associated
                    with the Nith substructure taken from the set
                    of identical substuctures STRU
                    
    Example 1 :
    ___________

      B1 = BASE STRU1 MOD1 ;              B1 is elementary
      B  = B1 ET B2 ET ....;
      FN1= PJBA B1       FORCE1 ;      |  Both formulations
      FN1= PJBA B STRU1  FORCE1 ;      |  are equivalent

    Example 2 :
    ___________

      STRU2= STRU1 RIGI2 MASS2 6 ;        STRU2 includes 6 identical
                                          substructures
      B2   = BASE STRU2 MOD2 ;
      FN2  = PJBA B2 STRU2 4 FORCE2 ;     B2 STRU2 4 stands for the
                                          elementary base connected 
                                          with the STRU2 4th 
                                          substructure.