data w;

array r[20];/*建立数组*/

r[1]=4;

do i=1 to 12;

r[i+1]=r+0.001*r*(1000-r);

end;

proc print;

data w;

do i=1 to 21;

input #i year num / y next@;/*读取差值*/

cha=next-num;

output;

end;

drop y;

datalines;

1790 3929000

1800 5308000

1810 7240000

1820 9638000

1830 12866000

1840 17069000

1850 23162000

1860 31443000

1870 38558000

1880 50156000

1890 62948000

1900 75995000

1910 91972000

1920 105711000

1930 122755000

1940 131669000

1950 150697000

1960 179323000

1970 203212000

1980 226505000

1990 248710000

2000 281416000

;

proc plot;

plot cha*num;

run;

输出结果：

data w;

array O[30] ;

array H[30];

O[1]=151;

H[1]=199;

do i=1 to 29;

O[i+1]=1.2*O-0.001*O*H;

H[i+1]=1.3*H-0.002*O*H;

end;

do i=1 to 30; /*将数组转化为列观测，便于画图*/

y=O;

z=H;

output;

end;

drop o1-o30 h1-h30;

proc gplot;

plot y*i z*i/overlay; /*overlay将两幅图叠加*/

run;

输出结果：