sch_add command

    (A) Function
        Registering a cell in a schedule list. 

    (B) Format

        sch_add  <time>  <key>  <script> {<argument>}

    (C) Parameters
        <time>
         Designate time to execute <script>. 
         Use an unsigned integer, a +-signed integer or a random number.
         A +-signed integer means that this command starts its execution 
         at the time that is the current simulation time plus the time 
         given by the integer here.
         For specifications by random numbers, use the following format. 
         Here, <min>, <max>, <mean> and <variance2> are all unsigned integers. 
             '%u' <min> ' ' <max>
                This denotes that time to execute this command is the simulation 
                time plus the time given by a random number (natural number) 
                between <min> and <max> in a uniform distribution.
             '%e' <min> ' ' <max> ' ' <mean>
                This denotes that time to execute this command is the simulation  
                time plus the time given by a random number (natural number) 
                between <min> and <max> in an exponential distribution with 
                a mean of <mean>.
             '%n' <min> ' ' <max> ' ' <mean> ' ' <variance2>
                This denotes that time to execute this command is the simulation
                time plus the time given by a random number (natural number) 
                between <min> and <max> in a normal distribution with a mean of
                <mean> and a variance of sqrt (<variance2>).

         <key>
           Designate the identifier of a cell created in a schedule list. 

         <script>
           This parameter is a script embedded in a token.

         <argument>
           This parameter is an argument to be passed to <script>.

    (D) Notes
        The time specified in <time> must be later than the simulation 
        time in the command.

        If <time> is an unsigned integer or a +-signed integer, set this 
        parameter with one token. If it is a random number, use 3 to 5 
        tokens depending on the type of the random number.

        It may take much time to obtain a proper value if a random number 
        specified in <time> has a small probability of lying between 
        <min> and <max>. (There may be an endless case.)

        Because seeds of random numbers are randomly chosen when SECONDS 
        starts up, you may have different simulation results with a same script.

        When <script> is executed, the eval command is called.
        The <script> parameter is assigned to the first argument 
        and <argument> is assigned to and after the second argument.

        You should describe a stage operating of a queue with SFL, 
        if simulating a queue of M/M/1 or others. For this simulation,
        you will use the schedule function whose execution time is 
        specified with the %e format and which enables to turn on and 
        off a value of an instruction terminal or a task.

        Cells created with the sch_add command are always inserted 
        at the ends of schedule lists. If you change a cell position 
        in a schedule list or move a cell to another schedule list, 
        use the sch_mv command.

    (E) Related items
        forward command
        eval command
        sch_mv command
        sch_rmv command
        schedule command