liukeyan 发表于 2008-3-21 15:55

dsolve的问题

dsolve('Dx+207*x-61*y=150*cos(800*pi*t)','Dy+83*y-61*x=15*cos(800*pi*t)','x(0)=0,y(0)=0','t')

这个应该能解吧？怎么解不出来啊？错在哪？

[ 本帖最后由 无水1324 于 2008-3-21 20:18 编辑 ]

无水1324 发表于 2008-3-21 20:20

ans =

    x:
    y:
.

我这里得到的结果

咕噜噜 发表于 2008-3-22 07:57

把里面的系数全都改为符号试试看

octopussheng 发表于 2008-3-22 09:53

用maple试试看！

liukeyan 发表于 2008-3-22 17:33

回复 楼主 的帖子

结果应该是个 时间函数，按说这是一个很常见的 二元微分方程组，挺基本的，matlab咋就算不出来？

咕噜噜 发表于 2008-3-22 18:55

是你自己没有把命令写全
x,y]=dsolve('Dx+207*x-61*y=150*cos(800*pi*t)','Dy+83*y-61*x=15*cos(800*pi*t)','x(0)=0,y(0)=0','t')

x =

-1/30260*(-8508384000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))*pi^2-13608897885*cos(800*pi*t)-5809920000000*pi^3*sin(800*pi*t)-1459016160000*cos(800*pi*t)*pi^2-112376562000*pi*sin(800*pi*t)+93696000000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2))*pi^4-93696000000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))*pi^4+8371152000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2))*pi^2+95232000000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2))*pi^4+8508384000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2))*pi^2-95232000000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))*pi^4+1038160080000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t+t*7565^(1/2))*pi^2+11619840000000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t-t*7565^(1/2))*pi^4+1038160080000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t-t*7565^(1/2))*pi^2+11619840000000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t+t*7565^(1/2))*pi^4-8371152000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))*pi^2-42122397*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))+82886007/2*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2))-82886007/2*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))+42122397*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2))+10279223655/2*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t+t*7565^(1/2))+10279223655/2*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t-t*7565^(1/2)))/(452929+91488000*pi^2+1024000000*pi^4)


y =

1/30260*(-8371152000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))*pi^2+12478641495*cos(800*pi*t)+580992000000*pi^3*sin(800*pi*t)-382728480000*cos(800*pi*t)*pi^2+11619840000000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t+t*7565^(1/2))*pi^4+11619840000000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t-t*7565^(1/2))*pi^4+1038160080000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t+t*7565^(1/2))*pi^2+1038160080000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t-t*7565^(1/2))*pi^2+202866066000*pi*sin(800*pi*t)-95232000000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2))*pi^4+95232000000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))*pi^4-8508384000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2))*pi^2+93696000000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2))*pi^4+8371152000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2))*pi^2-93696000000*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))*pi^4+8508384000*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))*pi^2+10279223655/2*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t+t*7565^(1/2))+10279223655/2*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*exp(-145*t-t*7565^(1/2))-82886007/2*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))-42122397*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2))+42122397*(-549841+16864000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t+t*7565^(1/2))+82886007/2*(599643+64288000*pi^2)/(452929+91488000*pi^2+1024000000*pi^4)*7565^(1/2)*exp(-145*t-t*7565^(1/2)))/(452929+91488000*pi^2+1024000000*pi^4)

咕噜噜 发表于 2008-3-22 18:57

如若换成符号
=dsolve('Dx+a*x-b*y=c*cos(d*t)','Dy+e*y-f*x=g*cos(d*t)','x(0)=0,y(0)=0','t')

[ 本帖最后由 咕噜噜 于 2008-3-22 18:59 编辑 ]
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