2.19                     ********************
                                 * EXTRMAP WRITE-UP *
                                 ********************
        
           Program EXTRMAP extracts a region from an input electron density 
        map prepared by FSFOUR, and writes it to a file in a form suitable for 
        input to any of the averaging programs (MAPORTH,MAPAVG,SKEW,LSQROT 
        etc.) The file can also be used in MAPVIEW if the non-fsfour map mode 
        is specified. This program is generally used to extract a 3D region 
        from the map which encompasses the dimer, trimer etc to be averaged, 
        i.e. a crystallographic asymmetric unit. There are no restrictions on 
        the specified output region, i.e. unit cell edges can be crossed, both 
        in the positive and negative direction. Note that the same thing can 
        be done with MAPVIEW in interactive mode, but EXTRMAP is better suited 
        for incorporation into a batch control file for multiple cycle runs. 
        
                             INPUT DATA (UNIT 5) 
        
        RECORD I    PAMFIL       (free format)
        
                    PAMFIL = Input parameter file, used only to get the
                             "running log" filename.
        
        
        
        RECORD II   INPMAP       (free format)
        
                    INPMAP = Input map file, as generated by FSFOUR
        
        
        
        RECORD III  OUTMAP       (free format)
        
                    OUTMAP = Output map file
        
        
        
        RECORD IV   XMIN, XMAX, YMIN, YMAX, ZMIN, ZMAX   (free format)
        
                    XMIN =
                    XMAX = 
                           Minimum and maximum coordinates, fractional
                    YMIN = 
                    YMAX = defining volume to be extracted and output.
        
                    ZMIN =
                    ZMAX =
        
        
        
                                   ***** FILES *****
        
        
        INPUT MAP FILE (BINARY) - standard FSFOUR output, in default
                                  orientation i.e. NORN=0 
                                                                  
        
        OUTPUT MAP FILE (BINARY) - contains extracted region
        
        record 1)  A,B,C,AL,BE,GA,NX,NY,NZ,IXMN,IYMN,IZMN,IXMX,IYMX,IZMX
        
        with first 6 values REAL*4, next 9 INTEGER*4, lengths in Angstroms,
        angles in degrees.
        
        NX = 
               Number of grid points defining one "cell length" along
        NY =    respective axis. Implicitly defines grid spacing as 
               del x = A/NX, del y = B/NY and del z = C/NZ
        NZ =
        
        IXMN, IXMX =  
                      Minimum, maximum grid index defining map region such
        IYMN, IYMX =  that  x (fractional) = IX * (del x) / A  etc. 
                      There are no restrictions on magnitudes or signs.
        IZMN, IZMX = 
        
        The map follows as (IYMX-IYMN+1)*(IZMX-IZMN+1) records, with
        each containing one row (IXMX-IXMN+1 REAL*4 values) along X,
        starting at IXMN. Y is slowest varying, i.e. the file could have
        been created with the following FORTRAN code:
        
               DO 30 IY=IYMN,IYMX
               DO 20 IZ=IZMN,IZMX
        20     WRITE(LU)(RHO(IX,IY,IZ),IX=IXMN,IXMX)
        30     CONTINUE