数学建模社区-数学中国

标题: 紧急！请教一个matlab问题 [打印本页]

作者: 枫回路转 时间: 2009-6-10 11:00
标题: 紧急！请教一个matlab问题
function xdot=shier(t,x)
a=0.01;
xdot=[(2-a*x(2)).*x(1);(-1+a*x(1)).*x(2)];

ts=0:0.1:15;
x0=[300,150];
[t,x]=ode23('shier',ts,x0);[t,x],
plot(t,x),grid,gtext('x(t)'),gtext('f(t)'),
pause,
plot(x(:,1),x(:,2)),grid,
我运行了，但一直提示未定义x
高手帮忙啊。

作者: mrx 时间: 2009-6-10 12:11
没有问题啊，首先定义m文件，然后运行
ts=0:0.1:15;
x0=[300,150];
[t,x]=ode23('shier',ts,x0);[t,x],
plot(t,x),grid,gtext('x(t)'),gtext('f(t)'),
pause,
plot(x(:,1),x(:,2)),grid,
运行结果

ans =
      0  300.0000  150.0000
0.1000  310.2387  184.3450
0.2000  308.6067  227.5985
0.3000  292.7688  278.5926
0.4000  263.2902  333.2592
0.5000  224.4162  385.0020
0.6000  182.4585  426.9149
0.7000  143.2651  454.3919
0.8000  110.3084  466.4394
0.9000 84.4936  464.9824
1.0000 65.1604  453.2371
1.1000 51.0330  434.5108
1.2000 40.8177  411.5467
1.3000 33.4470  386.4073
1.4000 28.1184  360.5242
1.5000 24.2578  334.8442
1.6000 21.4640  309.9672
1.7000 19.4598  286.2549
1.8000 18.0543  263.9089
1.9000 17.1159  243.0249
2.0000 16.5565  223.6262
2.1000 16.3176  205.6939
2.2000 16.3604  189.1810
2.3000 16.6660  174.0232
2.4000 17.2234  160.1474
2.5000 18.0355  147.4733
2.6000 19.1196  135.9312
2.7000 20.4937  125.4510
2.8000 22.1850  115.9552
2.9000 24.2356  107.3797
3.0000 26.6897 99.6613
3.1000 29.6093 92.7463
3.2000 33.0636 86.5866
3.3000 37.1343 81.1394
3.4000 41.9219 76.3726
3.5000 47.5340 72.2586
3.6000 54.1059 68.7844
3.7000 61.7770 65.9422
3.8000 70.7183 63.7457
3.9000 81.1009 62.2160
4.0000 93.1208 61.4094
4.1000  106.9687 61.3934
4.2000  122.8183 62.3015
4.3000  140.8273 64.2987
4.4000  161.0449 67.6449
4.5000  183.4188 72.6906
4.6000  207.6195 79.9629
4.7000  232.9878 90.1794
4.8000  258.3297  104.3254
4.9000  281.6921  123.6977
5.0000  300.2902  149.8268
5.1000  310.6166  184.1830
5.2000  309.0228  227.5048
5.3000  293.1752  278.5718
5.4000  263.6744  333.3456
5.5000  224.7128  385.2315
5.6000  182.6451  427.2722
5.7000  143.3545  454.8329
5.8000  110.3249  466.9180
5.9000 84.4650  465.4504
6.0000 65.1100  453.6728
6.1000 50.9717  434.9054
6.2000 40.7534  411.8942
6.3000 33.3835  386.7083
6.4000 28.0572  360.7820
6.5000 24.1993  335.0632
6.6000 21.4081  310.1518
6.7000 19.4060  286.4095
6.8000 18.0017  264.0379
6.9000 17.0638  243.1309
7.0000 16.5049  223.7118
7.1000 16.2651  205.7622
7.2000 16.3071  189.2338
7.3000 16.6105  174.0621
7.4000 17.1672  160.1758
7.5000 17.9778  147.4947
7.6000 19.0583  135.9460
7.7000 20.4266  125.4567
7.8000 22.1111  115.9502
7.9000 24.1548  107.3654
8.0000 26.6019 99.6402
8.1000 29.5117 92.7176
8.2000 32.9566 86.5513
8.3000 37.0149 81.0968
8.4000 41.7893 76.3231
8.5000 47.3861 72.2015
8.6000 53.9405 68.7193
8.7000 61.5930 65.8684
8.8000 70.5120 63.6618
8.9000 80.8732 62.1209
9.0000 92.8667 61.2999
9.1000  106.6914 61.2691
9.2000  122.5164 62.1544
9.3000  140.5052 64.1252
9.4000  160.7131 67.4327
9.5000  183.0737 72.4423
9.6000  207.2876 79.6625
9.7000  232.7042 89.8082
9.8000  258.1065  103.8719
9.9000  281.5872  123.1382
10.0000  300.3794  149.1461
10.1000  310.9267  183.3986
10.2000  309.5745  226.6349
10.3000  293.9649  277.6968
10.4000  264.5836  332.6163
10.5000  225.6129  384.7519
10.6000  183.4347  427.1045
10.7000  143.9736  454.9769
10.8000  110.7690  467.3095
10.9000 84.7735  466.0281
11.0000 65.3038  454.3601
11.1000 51.0877  435.6285
11.2000 40.8169  412.6151
11.3000 33.4119  387.4025
11.4000 28.0622  361.4356
11.5000 24.1884  335.6696
11.6000 21.3857  310.7088
11.7000 19.3750  286.9167
11.8000 17.9643  264.4958
11.9000 17.0216  243.5424
12.0000 16.4570  224.0810
12.1000 16.2126  206.0911
12.2000 16.2492  189.5258
12.3000 16.5476  174.3208
12.4000 17.0957  160.4006
12.5000 17.9005  147.6897
12.6000 18.9734  136.1166
12.7000 20.3317  125.6019
12.8000 22.0081  116.0755
12.9000 24.0383  107.4707
13.0000 26.4708 99.7245
13.1000 29.3660 92.7846
13.2000 32.7892 86.5990
13.3000 36.8284 81.1285
13.4000 41.5748 76.3363
13.5000 47.1452 72.1988
13.6000 53.6647 68.6977
13.7000 61.2815 65.8299
13.8000 70.1583 63.6017
13.9000 80.4722 62.0409
14.0000 92.4183 61.1926
14.1000  106.1820 61.1354
14.2000  121.9573 61.9878
14.3000  139.8824 63.9189
14.4000  160.0433 67.1735
14.5000  182.3574 72.1162
14.6000  206.5651 79.2416
14.7000  231.9880 89.2736
14.8000  257.4728  103.1830
14.9000  281.1288  122.2532
15.0000  300.1625  148.0108

作者: mrx 时间: 2009-6-10 12:14

作者: 陈文龙 时间: 2009-6-10 12:21
应该把建立函数单独放在一个M文件中,然后运行后面的程序就可以了

作者: madio 时间: 2009-6-10 12:32
我运行了，没有问题，我估计你是没有把定义的函数shier，保存为M文件，所以后面没有办法调用！

untitled.jpg (36.45 KB, 下载次数: 236)

作者: lyg1234 时间: 2009-6-10 13:21
matlab中用function自定义的函数shier应该单独保存为一个m文件：shier.m

你要解决的是那个地中海鲨鱼和食用鱼所构成的食饵-捕食者模型的程序吧，一看图形就觉得眼熟，呵呵

欢迎光临数学建模社区-数学中国 (http://www.madio.net/)