MATLAB: What is wrong with the code

iteration

I am currently doing a school project where i have to plot the trajectory of a projectile launched from the ground with initial speed V0, and angle theta above the horizontal. The projectile has to hit a target distance D=10000m away once it has reached the ground. I have used an initial guess of theta=pi/30 as the angle, so that the projectile does not reach D. The program should then automatically pick a new value of theta. I am doing this by increasing theta from pi/30 in steps dtheta=0.1 until the target is overshot. However, after plotting, I keep getting a wrong and wild graph. Here is my code:
    %contants
    D=10000;
    u=600;
    m=50;
    g=9.81;
    %initial conditions
    theta=pi/30;
    x=0;
    i=0;
    t=0;
    y=0;
    dtheta=0.1;
    dt=0.1;
    while x(i+1)<D
    for i=1:1000
    xdot(i)=u*cos(theta);
    ydot(i)=u*sin(theta);
    v(i)=sqrt(xdot(i).^2+ydot(i).^2);
    x(i+1)=(t.*xdot(i));
    y(i+1)=(t.*ydot(i))-(0.5*g*(t.^2));
    xdbldot(i)=0; 
    ydbldot(i)=-g;
    vel_x(i+1)=xdot(i)+(t.*xdbldot(i));
    vel_y(i+1)=ydot(i)+(t.*ydbldot(i));
    t=t+dt;
    if y(i+1)<0
        break
    end
    end
    if x(i+1)<D
    theta=theta+dtheta;
    if x(i+1)>D
        break
    end
    end
    end
    plot(x,y),grid
    xlabel('Distance/[m]')
    ylabel('Height/[m]')

Best Answer

I think maybe you want this:
x(i+1)=x(i) + (t.*xdot(i));
y(i+1)=y(i) + (t.*ydot(i))-(0.5*g*(t.^2));
when you update x and y.
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