Help using solve function with inputting a known variable

1 次查看（过去 30 天）

Ian 2011-2-7

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/927-help-using-solve-function-with-inputting-a-known-variable

Hello all,

I'm using the solve function to solve a system of non-linear equations and I'm having a little trouble. I'm trying to input a function f into one of the equations, and then solve for the 3 variables. The problem is that it treats f as a symbolic variable. The order is also messed up, but I think I just need to specifically call the solutions for each variable.

Here is the code:

function kinematicanal

clc;

syms x1 y1 phi1;

for k=1:1:11

    t=(k-1)/10;
    f=sin(10*t);
    [x1sol(k),y1sol(k),phi1sol(k)]=solve('x1-sin(phi1)','y1+cos(phi1)','phi1-f',x1,y1,phi1);

q=[x1sol;y1sol;phi1sol];

end

Can anyone help? Thanks, Ian

Edit: That should be a bit easier to read the code

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。

采纳的回答

Walter Roberson 2011-2-7

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/927-help-using-solve-function-with-inputting-a-known-variable#answer_1336

在 MATLAB Online 中打开

[x1sol(k), y1sol(k), phi1sol(k)] = solve(x1-sin(phi1), y1+cos(phi1), phi1-f, x1, y1, phi1);

Question: why do you bother constructing q within the loop? You overwrite it each time through the loop, and you overwrite it with the complete vectors, so the end result would be the same as constructing it once after the loop.

Question 2: why are you not pre-allocating space for x1sol, y1sol, phi1sol?

Question 3: why do you not just do the solve() once outside of any loop, with k symbolic? You would get out a single x1sol, y1sol, phi1sol that was parameterized in terms of k. matlabFunction() the result if you need to, and feed it 1:11 and you will get all the answers at once.

Question 4: if t = (k-1)/10 and f=sin(10*t) and you do not use t for anything else, then why not skip t and go directly for f = sin(k-1) ?

Question 5: are you sure you want to be taking the sin() of an integer number of radians???