How can I change variables in for loop in order to use the variables in subs?

Question

MS 2013-11-29

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/107992-how-can-i-change-variables-in-for-loop-in-order-to-use-the-variables-in-subs

评论： MS 2013-11-29

采纳的回答： David Sanchez

在 MATLAB Online 中打开

I would like to find out intersection (coordinate) between circle and line.

One thing remarked is that

I want to change the slope of the line by change 'th' in for loop as shown below code, so that I will have matrix of intersection coordinates.

The problem is that when function 'subs' replace the 'th' in eq. as looping over, it does not evaluate 'xc' and 'yc'.

I want to have exact numeric result such as

xc = 365

yc = -235

but the result returns like

xc = -((350*tan(th)*(tan(th)^2 - 3)^(1/2) + 700)/(tan(th)^2 + 1) - 700)/tan(th) ((350*tan(th)*(tan(th)^2 - 3)^(1/2) - 700)/(tan(th)^2 + 1) + 700)/tan(th)

Anything I am missing?

Thanks in advance.

if true
  % code
end
syms x y a thr;
eq1='x^2+y^2=a^2'
eq2='y=tan(th)*x-2*a'
[xc,yc]=solve(eq1,eq2,x,y)
k=1;
for th=0:90 %count the number of th
  k=k+1;
end
k=k-1;
th=0:90; %th matrix
for s=1:k
  th(s)=th(s)*pi/180;
  subs(xc,{a,th},{350,th(s)})
  subs(xc,{a,th},{350,th(s)})
end

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Answer 1

David Sanchez 2013-11-29

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/107992-how-can-i-change-variables-in-for-loop-in-order-to-use-the-variables-in-subs#answer_116705

在 MATLAB Online 中打开

Look at the code below and see the differences with yours. The one below returns what you want.

syms x y a thr;
eq1='x^2+y^2=a^2';
eq2='y=tan(thr)*x-2*a';
[xc,yc]=solve(eq1,eq2,x,y);
th=0:90; %th matrix
k = length(th);
for s=1:k
  th(s)=th(s)*pi/180;
  subs(xc,{a,thr},{350,th(s)})
  subs(xc,{a,thr},{350,th(s)})
end