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标题: 求解常微分方程遇到的问题 [打印本页]

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作者: 木星流火    时间: 2014-8-14 10:23
标题: 求解常微分方程遇到的问题
clc,clear
dsolve('m*D2s=m*g-rou*g*V-k*Ds','Ds(0)=0','t')
m=239.46;g=9.8;rou=1035.71;V= 0.2058;k=0.6;
运行结果
ans =

(g*m*(m - V*rou))/(k^2*exp((k*t)/m)) - ((C4*exp((k*t)/m))/k^2 - (g*t*exp((k*t)/m)*(m - V*rou))/k)/exp((k*t)/m)
怎样将m、g等的值代入？

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作者: madio    时间: 2014-8-14 15:52

1. clc,clear
   
2. syms m g rou V k s
   
3. s=dsolve('m*D2s=m*g-rou*g*V-k*Ds','Ds(0)=0','t');
   
4. m=239.46;g=9.8;rou=1035.71;V= 0.2058;k=0.6;
   
5. subs(s)

复制代码

你应该要这样去写！

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作者: MCR董事长    时间: 2014-8-14 15:52
>> dsolve('m*D2s=m*g-rou*g*V-k*Ds','Ds(0)=0','t')
ans =
(m*exp(-(k*t)/m)*(g*m - V*g*rou))/k^2 - exp(-(k*t)/m)*((C4*exp((k*t)/m))/k^2 - (t*exp((k*t)/m)*(g*m - V*g*rou))/k)
>> m=239.46;g=9.8;rou=1035.71;V= 0.2058;k=0.6;
>> b=subs(ans)
b =
(188578330473244179*exp(-(10*t)/3991))/1099511627776 + exp(-(10*t)/3991)*((236254485684345*t*exp((10*t)/3991))/549755813888 - (25*C4*exp((10*t)/3991))/9)

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作者: MCR董事长    时间: 2014-8-14 15:52
>> dsolve('m*D2s=m*g-rou*g*V-k*Ds','Ds(0)=0','t')
ans =
(m*exp(-(k*t)/m)*(g*m - V*g*rou))/k^2 - exp(-(k*t)/m)*((C4*exp((k*t)/m))/k^2 - (t*exp((k*t)/m)*(g*m - V*g*rou))/k)
>> m=239.46;g=9.8;rou=1035.71;V= 0.2058;k=0.6;
>> b=subs(ans)
b =
(188578330473244179*exp(-(10*t)/3991))/1099511627776 + exp(-(10*t)/3991)*((236254485684345*t*exp((10*t)/3991))/549755813888 - (25*C4*exp((10*t)/3991))/9)

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