求助：如何把计算结果中的符号用其数值替换

gaoshuai008

我是新手，刚开始学习matlab。编了矩阵微分方程解析解的小程序，发现计算的最终结果里面全是是矩阵元素符号，我希望把他变成其相应的数值，请问该怎么弄呢？网上查了好久都没查到，急啊...请各位大神指点。以下是我编的程序以及结果（结果太长了，随便截了点，但是形式就是这样的）：
clear all
clc
syms t x y
M=[1 2;
      2 1;];
K=[3 4;
      4 3;];
[x,y]=dsolve('M(1,1)*D2x+M(1,2)*D2y+K(1,1)*x+K(1,2)*y=0',...
                'M(2,1)*D2x+M(2,2)*D2y+K(2,1)*x+K(2,2)*y=0')

x =

-(C1*M(1,1)*exp(1/2*(-(-2*K(1,2)*M(2,1)+2*M(1,1)*K(2,2)+2*M(2,2)*K(1,1)-2*K(2,1)*M(1,2)-2*(M(2,1)^2*K(1,2)^2-2*M(2,1)*K(1,2)*M(1,1)*K(2,2)-2*M(2,2)*K(1,1)*M(2,1)*K(1,2)-2*K(2,1)*M(1,2)*M(2,1)*K(1,2)+M(1,1)^2*K(2,2)^2-2*M(2,2)*K(1,1)*M(1,1)*K(2,2)-2*K(2,1)*M(1,2)*M(1,1)*K(2,2)+M(2,2)^2*K(1,1)^2-2*M(2,2)*K(1,1)*K(2,1)*M(1,2)+K(2,1)^2*M(1,2)^2+4*M(1,1)*K(2,1)*M(2,2)*K(1,2)+4*M(2,1)*K(1,1)*K(2,2)*M(1,2))^(1/2))/(M(1,1)*M(2,2)-M(1,2)*M(2,1)))^(1/2)*t)*K(2,2)*(-(-2*K(1,2)*M(2,1)+2*M(1,1)*K(2,2)+2*M(2,2)*K(1,1)-2*K(2,1)*M(1,2)-2*(M(2,1)^2*K(1,2)^2-2*M(2,1)*K(1,2)*M(1,1)*K(2,2)-2*M(2,2)*K(1,1)*M(2,1)*K(1,2)-2*K(2,1)*M(1,2)*M(2,1)*K(1,2)+M(1,1)^2*K(2,2)^2-2*M(2,2)*K(1,1)*M(1,1)*K(2,2)-2*K(2,1)*M(1,2)*M(1,1)*K(2,2)+M(2,2)^2*K(1,1)^2-2*M(2,2)*K(1,1)*K(2,1)*M(1,2)+K(2,1)^2*M(1,2)^2+4*M(1,1)*K(2,1)*M(2,2)*K(1,2)

y =

(-M(2,1)*exp(1/2*(-(-2*K(1,2)*M(2,1)+2*M(1,1)*K(2,2)+2*M(2,2)*K(1,1)-2*K(2,1)*M(1,2)-2*(M(2,1)^2*K(1,2)^2-2*M(2,1)*K(1,2)*M(1,1)*K(2,2)-2*M(2,2)*K(1,1)*M(2,1)*K(1,2)-2*K(2,1)*M(1,2)*M(2,1)*K(1,2)+M(1,1)^2*K(2,2)^2-2*M(2,2)*K(1,1)*M(1,1)*K(2,2)-2*K(2,1)*M(1,2)*M(1,1)*K(2,2)+M(2,2)^2*K(1,1)^2-2*M(2,2)*K(1,1)*K(2,1)*M(1,2)+K(2,1)^2*M(1,2)^2+4*M(1,1)*K(2,1)*M(2,2)*K(1,2)+4*M(2,1)*K(1,1)*K(2,2)*M(1,2))^(1/2))/(M(1,1)*M(2,2)-M(1,2)*M(2,1)))^(1/2)*t)*C3*K(1,2)*(-(-2*K(1,2)*M(2,1)+2*M(1,1)*K(2,2)+2*M(2,2)*K(1,1)-2*K(2,1)*M(1,2)-2*(M(2,1)^2*K(1,2)^2-2*M(2,1)*K(1,2)*M(1,1)*K(2,2)-2*M(2,2)*K(1,1)*M(2,1)*K(1,2)-2*K(2,1)*M(1,2)*M(2,1)*K(1,2)+M(1,1)^2*K(2,2)^2

qibbxxt

1# gaoshuai008

1. [x,y]=dsolve('D2x+2*D2y+3*x+4*y=0',...
   
2. '2*D2x+D2y+4*x+3*y=0');

复制代码

1. 
   
2. >> x
   
3. 
   
4. x =
   
5. 
   
6. (21^(1/2)*C5*cos((21^(1/2)*t)/3))/7 - C7*sin(t) - C8*cos(t) + (21^(1/2)*C6*sin((21^(1/2)*t)/3))/7
   
7. 
   
8. >> y
   
9. 
   
10. y =
    
11. 
    
12. C8*cos(t) + C7*sin(t) + (21^(1/2)*C5*cos((21^(1/2)*t)/3))/7 + (21^(1/2)*C6*sin((21^(1/2)*t)/3))/7
    

复制代码

gaoshuai008

多谢斑竹出售相救啊！
我想要结果能随矩阵值的不同而结果不同，如果像您这样改的话，每次遇到不同的矩阵都必须手动改掉dsolve（）里面的系数，有点麻烦。不知道如何让dsolve里面的系数与矩阵元素关联，而结果显示是数值？有没有这种方法，或者是我的想法就是错的？恳请大神指点迷津啊！！！
2# qibbxxt

mhkmars

3# gaoshuai008
用匿名函数可以很方便的进行参数传递，此外你也可以在版内搜索关键词
参数传递
非线性方程
之类的，里面讨论有很多的

gaoshuai008

多谢指点，我去看看 4# mhkmars