Models Controls

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Control statements in Models

The MODELS language supports four types of control structures
1. IF
2. FOR
3. DO
4. WHILE

1. if - then - else - elseif - endif

This example illustrates how to used the IF structure in MODELS.

MODEL if_example

VAR k

INIT
k:=0
ENDINIT

EXEC
if k=0 then
    k:=1
elsif k=1 then
    write("In first 'elsif' with k=1")
    k:=2
elsif k=2 then
    write("In second 'elsif' with k=2")
    k:=3
else
    write("In 'else' with k=3")
endif
ENDEXEC
ENDMODEL

2. for - to - by - do - endfor

This example illustrated the usage of the FOR statement in MODELS.

MODEL for_example

VAR k

EXEC
IF t=timestep THEN       -- letting contents execute only at the first time step

write("*** Begin results of model 'for_example' ***")

FOR z10:=0 TO 5, 6, 7 TO 9 BY 1   -- 3 value groups: 0 to 5      : 0,1,2,3,4,5
                                    --                 6           : 6
                                    --                 7 to 9 by 1 : 7,8,9
FOR z1:=0 TO 8 BY 2   -- 1 group of values: 0,2,4,6,8
DO
   k:=z10*10 +z1        -- 0,2,4,6,8,10,12,14,16,18,20,22,24,...,94,96,98
   write(k)
ENDFOR

FOR z10:=9 to 0 by -1     -- 1 group of values: 9,8,7,6,5,4,3,2,1,0
FOR z1:=5, 0              -- 2 groups of single values (call it a list?): 5, 0
DO write(z10*10 +z1)      -- 95,90,85,80,75,...,15,10,5,0
ENDFOR

FOR n:= 1 to 4
FOR m:= n to 4
DO write( m ) -- 1,2,3,4, 2,3,4, 3,4, 4
ENDFOR

write("*** End results of model 'for_example' ***")
ENDIF
ENDEXEC
ENDMODEL

3. do - redo - enddo

This example illustated the DO structure in MODELS.

MODEL do_example

VAR k

EXEC
IF t=timestep THEN       -- letting contents execute only at the first time step
write("*** Begin results of model 'do_example' ***")
k:=5
DO
    write('k=', k, ' in loop ')
    k:=k-1
    IF k>0 THEN REDO     -- jump up to DO statement
    ENDIF
ENDDO
write('k=', k, ' after loop ')
write("*** End results of model 'do_example' ***")
ENDIF
ENDEXEC
ENDMODEL

4. while - do - endwhile

This example illustrates the use of WHILE..ENDWHILE in MODELS.

MODEL while_example

VAR k

EXEC
IF t=timestep THEN       -- letting contents execute only at the first time step
write("*** Begin results of model 'while_example' ***")
k:=5
WHILE k>0 DO
    write('k=', k, ' in loop ')
    k:=k-1
ENDWHILE
write('k=', k, ' after loop ')
write("*** End results of model 'while_example' ***")
ENDIF
ENDEXEC
ENDMODEL