Solving an equation to get a particular solution

Question

onsagerian 2018-9-2

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/417204-solving-an-equation-to-get-a-particular-solution

评论： Star Strider 2018-9-3

Hello,

The following code was designed to solve a particular equation depending on a variable "n", which gives many solutions(both positive and negative) for each n. However, my objective is to get only positive solutions corresponding to each n. Would you let me know what command I should include to get such solutions?

format long e
T=0.1;
k=1.0;        
k_1=0.2;      
k_2=0.1;      
%k_2=[0.1:0.1:1.0];
a_p=0.0001;     
k_p=a_p/10;   
a_q=0.00015;   
k_q=0.00002;    
theta=0.01;               
m1=0.0000005;             
m2=0.0000002;            
W=0.00002;               
syms x
gamma=(a_p*k*k_2)/(k_p*m1*k_1);
for n=1:1:10
equation=[(1+sqrt(gamma*theta^n))/sqrt(gamma+sqrt(theta^n))]^2-[(theta+x)/(1+x)]^(n+1)==0;  
sol=solve(equation,x);   <======= Any additional command to get positive solutions? 
fprintf('%d\n',n);
fprintf('%.10e\n',sol);
end

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Star Strider 2018-9-2

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/417204-solving-an-equation-to-get-a-particular-solution#answer_335112

在 MATLAB Online 中打开

Use vpasolve to get all the results, then in the second fprintf call, simply choose the values of ‘sol’ greater than zero to get only the positive solutions:

for n=1:1:10
    equation=[(1+sqrt(gamma*theta^n))/sqrt(gamma+sqrt(theta^n))]^2-[(theta+x)/(1+x)]^(n+1)==0;
    sol=vpasolve(equation,x);   % <======= Any additional command to get positive solutions?
    fprintf('%d\n',n);
    fprintf('%.10e\n',sol(sol > 0));
end