why complex value appears in this array

Question

ttopal 2016-7-6

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/293927-why-complex-value-appears-in-this-array

评论： ttopal 2016-7-6

Hi guys.

I am quite new to matlab and I have been spending all my day to figure out why this simple code wont work. I am sure there are easier ways to solve this problem but what I would like to do is create a point set in x,y coordinates. Anyways up to 4th condition code works, when it goes to 4th condition (when idx is 46) y values becomes complex and there is no reason. yyy temp calculation should be equal to y(46). Any ideas? Thanks in advance.

%create point set in cartesian plane(xi,yi)
r1 = 20;
r2 = 12;
rt = 2*(r1+r2);
length = 3*r1+2*r2;
x1 = [0:1:length];
idx = 1;
while idx <= 46
      if x1(idx)<= r1
          y(idx)= sqrt(r1^2-x1(idx)^2);
      elseif r1 < x1(idx) <= r1+r2
          y(idx)= -1*(sqrt(r2^2-(r2+r1-x1(idx))^2));        
      elseif r1+r2 < x1(idx) <= r1+2*r2
          y(idx)= -1*(sqrt(r2^2-(x1(idx)-r1-r2)^2));
      elseif r1+2*r2 < x1(idx) <= 2*r1+2*r2
          temp1=r1^2
          temp2=rt-x1(idx)
          temp3=temp2^2
          y(idx)= sqrt(temp1-temp3)   
      else 
          temp4=r1^2;
          temp5=x1(idx)-rt;
          temp6=temp2^2;
          y(idx)= sqrt(temp1-temp3);
      end
      idx = idx+1;
  end
  x1(46)
  y(46)
          temp1=r1^2
          temp2=rt-x1(46)
          temp3=temp2^2
          yyy= sqrt(temp1-temp3)