Solving Differential Equation with initial conditions

3 次查看（过去 30 天）
onsagerian
onsagerian 2018-2-10
评论： Star Strider 2018-2-11
Hello,
I tried to make a simple code for solving a coupled differential equation with initial conditions, but I got the following errors.(two separate errors) Would you check my code with the error message and make a correction?
syms S_1(t) S_2(t);
K=1;
k_1=20;
k_2=5;
k_3=5;
k_4=5;
k_5=2;
n=4;
S_1(0)=0.0;
S_2(0)=0.6;
dsolve(diff(S_1,t)==k_1*S_2^n/(K^n+S_2^n)-k_3*S_1-k_5*S_1)
dsolve(diff(S_2,t)==k_2+k_5*S_1-k_4*S_2)
Error using sym/subsasgn (line 942)
Invalid indexing or function definition. Indexing must follow MATLAB indexing. Function arguments must be symbolic variables, and function body must be sym expression.
Error in cal_test11 (line 10)
S_1(0)=0.0;

请先登录，再回答此问题。

采纳的回答

Star Strider
Star Strider 2018-2-10
You need to add the initial conditions as arguments to dsolve, and use the ‘double equal’ to assign them:
S_1s = dsolve(diff(S_1,t)==k_1*S_2^n/(K^n+S_2^n)-k_3*S_1-k_5*S_1, S_1(0)==0.0)
S_2s = dsolve(diff(S_2,t)==k_2+k_5*S_1-k_4*S_2, S_2(0)==0.6)
  5 个评论
显示 3更早的评论
onsagerian
onsagerian 2018-2-11
Thank you all for your explanation. I will see the documents.
Star Strider
Star Strider 2018-2-11
My pleasure.
Those links completely describe the code needed to convert your symbolic ODEs to anonymous functions.
Do not include the initial conditions ‘S_1(0)’ and ‘S_2(0)’ in the code you send to odeToVectorField. You will set the initial conditions as arguments to the ODE solver you choose.

请先登录，再进行评论。

更多回答（0 个）

类别

在 Help Center 和 File Exchange 中查找有关 Numeric Solvers 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by