LET

        [SIC\]LET Variable [=] [Expression]
        [SIC\]LET Variable [=] Expression /NEW Type [Attr]
        [SIC\]LET Variable [=] Expression /WHERE Condition_mask
        [SIC\]LET Variable [=] Expression /PROMPT "Explanatory text"
        [SIC\]LET Variable [=] Expression /RANGE Min Max
        [SIC\]LET Variable [=] Expression /CHOICE Value_1 ... Value_n
        [SIC\]LET Variable [=] Expression /INDEX Value_1 ... Value_n
        [SIC\]LET Variable [=] Expression /FILE Filter
        [SIC\]LET Variable [=] Expression /SEXAGESIMAL
        [SIC\]LET Variable [=] Expression /LOWER
        [SIC\]LET Variable [=] Expression /UPPER
        [SIC\]LET Variable [=] Expression /FORMAT format_string
        [SIC\]LET Variable [=] Expression /FORMULA
        [SIC\]LET Variable [=] OldVariable /REPLACE
        [SIC\]LET Variable /STATUS Read|Write

    Assign  a value to a variable. The variable must already be defined (see
    DEFINE) unless the /NEW option is present.  Logical  expression  results
    cannot be assigned to non logical variables, and vice versa. All numeri-
    cal expression evaluations are done in double precision,  and  automati-
    cally converted to the type of (numerical) variable assigned.

    The  equal sign may be always omitted EXCEPT when using Free Syntax (see
    below).

    If no value is assigned to the Variable, the user will be  prompted  for
    the  variable value. The Prompt text can be defined with the /PROMPT Op-
    tion.

    VECTOR OPERATION:

    Operations are vectorial, i.e. a full array  is  computed  at  the  same
    time. The variable name can define a subset of an known array, such as:
        DEFINE REAL A[4,5,6] B[4]
        LET A[,,3]  = 1.0  ! or equivalently  LET A[3] = 1.0
        LET A[,2,2] = B    ! or equivalently  LET A[2,2] = B
    These  commands  assign the value 1.0 to A[i,j,3], with i running from 1
    to 4 and j from 1 to 5, and B[k] to A[k,2,2] for k from 1 to 4.  Implic-
    it  transposition  is  now  allowed, though still somewhat experimental:
    both A[,2,3] and A[2,,3] are valid. A range of indexes can be  specified
    rather than one index: for the above example A[3:5] is a valid 4x5x3 ar-
    ray, A[2:4,,] is a 3x5x6 array.

    IMPLICIT LOOPS:

    In addition to vector computing, it is possible to assign an array using
    "implicit loops", i.e. functions of the array indices such as
        DEFINE REAL A[4,5]
        LET A[I,J] = (I-J)**2
    Implicit loops cannot be mixed with variable index values.

    CONDITION MASK (/WHERE option):

    Vector  assignment  can be done only where a specified logical array (or
    logical array expression) is true, using the /WHERE option. See HELP LET
    /WHERE.

    FREE SYNTAX:

    The  LET  command may be omitted if no option is present, and is the SIC
    syntax is set to FREE. In case of conflict between a variable name and a
    (complete) command name, an error message is issued. See SIC command.

    GUI (Graphic-User-Interface) input mode:

    If  command  GUI\PANEL  has  been issued before, the LET command defines
    widgets in the master window defined by GUI\PANEL. The widget is a  sim-
    ple  prompt  when  option  /PROMPT  is set, a slider if option /RANGE is
    present, a list of choices if option /CHOICE or /INDEX is given,  and  a
    selection of files with the specified filter when option /FILE is speci-
    fied. If neither of these options is present, the LET command  works  in
    the usual way.

    The  widgets are created and activated by command GUI\GO. Standard input
    can be used, and pressing button GO will define  all  the  variables  as
    specified. If button ABORT is pressed instead, none of the variables are
    modified and an error is returned. Error handling is available.