My plot comes out to be discontinuous

Hello, I have been trying to get a continuous plot but I couldn't. There are some discontinuities in my plot at the t values which the user inputs. and I couldn't find out the reason. Could you please help me? Thank you.

P.S.: The plot function is at the end of the code.

n = input('Enter the number of points: ');

    for j = 1:n
        
        str1 = [' Enter the time value of the point ' num2str(j) ': ']; 

        t(1,j) = input(str1);
        

    end
t

 for i = 1:n
        
        str2 = [' Enter the theta value of the point ' num2str(i) ': '];
        
        theta(1,i)=input(str2);

    end
theta


 for h = 1:n-2 % thetadots
           thetadot(1)=0;
          if sign(theta(h+1)-theta(h)) ~= sign(theta(h+2)-theta(h+1))
              thetadot(h+1)=0;
          elseif sign(theta(h+1)-theta(h)) == sign(theta(h+2)-theta(h+1))
              thetadot(h+1)=((theta(h+1)-theta(h))/(t(h+1)-t(h))+(theta(h+2)-theta(h+1))/(t(h+2)-t(h+1)))/2;
          end
            thetadot(n)=0;

 end
  

% theta(t)=a0+a1.*t+a2.*t.^2+a3.*t.^3

%a0=theta0
%a1=theta0dot
%a2=3./(tf.^2)*(thetaf-theta0)-2./tf*theta0dot-1./tf*thetafdot
%a3=-2./(tf.^3)*(thetaf-theta0)+1./(tf.^2)*(thetafdot+theta0dot)

tn=linspace(t(1),t(n),1000);
figure
hold on



for g = 1:n-1 %segments
    
  idx1= (t(g)<=tn & tn<=t(g+1));
  s1=theta(g)+thetadot(g).*(tn-t(g))...
  +((3/((t(g+1)-t(g))^2)*(theta(g+1)-theta(g))-(2/(t(g+1)-t(g)))*thetadot(g)-(1/(t(g+1)-t(g)))*thetadot(g+1))).*((tn-t(g)).^2) ...
  +((-2/((t(g+1)-t(g))^3)*(theta(g+1)-theta(g))+(1/((t(g+1)-t(g))^2))*(thetadot(g+1)+thetadot(g)))).*((tn-t(g)).^3);
        plot(tn(idx1),s1(idx1), 'LineWidth',2);
        xlabel('t (s)');
        ylabel('theta (deg)');
end

Answer 1

[Cris LaPierre]

The problem is that linspace most likely is not creating a vector that only contains the user inputted values at the beginning and end. Let's say t=[2 3 4 5 ... 15]. If I inspect the interval around 3, I see that tn = [... 2.963 2.976 2.989 3.002 3.015 3.028 ...].

When creating indx1, the first segment with end at 2.989 but the second will start at 3.002. Visually, this will appear as a gap between these two points.

Your easiest solution is to create tn inside your for loop for each segment. That way, the end points always match the previous and next segments, and your "resolution" is less affected by the value of n.

[alexrecai]

This solved my problem! Thank you very much