'
' Darwin's elephants
'
' elephants live to > age 100, and female elephants produce one offspring
' every 10 years from the age of 30 through 80 ( 6 in all ).
' The sex of the offspring sequence is determined by SEX(0) - SEX(5), with
' 0 being male, 1 being female.
'
' POP( sex, age/10 ) carries the population for each sex and age group.
'
' If sex(0-3)=1, sex(4)=0, sex(5)=1 (1=female, 0= male)
' this produces almost exactly 15 million elephants after 500 years!
' This is the maximum population possible.
'
'
DIM MALEPOP AS LONG
DIM FEMALEPOP AS LONG
DIM POP(1, 10) AS LONG

POP(0, 0) = 1   'initial male population
POP(1, 0) = 1   'initial female population
RSTART = 3      ' min age (age/10) of reproduction
RSTOP = 8       ' max age (age/10) of reproduction
SEX(0) = 1      ' sex of offspring of female aged RSTART
SEX(1) = 1      ' sex of offspring of female aged RSTART+1
SEX(2) = 1      ' sex of offspring of female aged RSTART+2
SEX(3) = 1      ' sex of offspring of female aged RSTART+3
SEX(4) = 0      ' sex of offspring of female aged RSTART+4
SEX(5) = 1      ' sex of offspring of female aged RSTART+5

PRINT "Years     Male pop.   Female pop.  Total pop.  Females/male."
FOR DECADE = 1 TO 50

  ' age the population by one decade, and count males aged RSTART to RSTOP
  ADULTMALEPOP = 0
  FOR AGE = 10 TO 1 STEP -1
    POP(0, AGE) = POP(0, AGE - 1)  'age the males by 10 years
    IF (AGE >= RSTART) AND (AGE <= RSTOP) THEN
      ADULTMALEPOP = ADULTMALEPOP + POP(0, AGE)
    END IF
    POP(1, AGE) = POP(1, AGE - 1)  'age the females by 10 years
  NEXT AGE
  POP(0, 0) = 0  'no newborn males yet
  POP(1, 0) = 0  'no newborn females yet

  ' if there are any male elephants, have each female between 30-80
  ' produce a son or daughter.
  IF ADULTMALEPOP > 0 THEN
    FOR AGE = RSTART TO RSTOP
      POP(SEX(AGE - RSTART), 0) = POP(SEX(AGE - RSTART), 0) + POP(1, AGE)
    NEXT AGE
  END IF
  ' print populations for each decade
  MALEPOP = 0
  FEMALEPOP = 0
  FOR AGE = 0 TO 10
    MALEPOP = MALEPOP + POP(0, AGE)
    FEMALEPOP = FEMALEPOP + POP(1, AGE)
  NEXT AGE
  PRINT DECADE * 10, STR$(MALEPOP), STR$(FEMALEPOP), STR$(MALEPOP + FEMALEPOP),
  IF MALEPOP > 0 THEN PRINT STR$(FEMALEPOP / MALEPOP);
  IF ADULTMALEPOP = 0 THEN PRINT " (no males)" ELSE PRINT

NEXT DECADE
END