论坛 › 数模问题互助 › 求解常微分方程遇到的问题

木星流火 发表于 2014-8-14 10:23

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？

madio 发表于 2014-8-14 15:52

clc,clear
syms m g rou V k s
s=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;
subs(s)你应该要这样去写！

MCR董事长 发表于 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)

MCR董事长 发表于 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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