Don't understand error

Working on a function that will determine the angle needed to launch a projectile at in order to hit a target, works like a newton solver. I have a script to run the function

for theta=0:0.1:pi
    V_int=380; % (m/s)
    target=400; % (meters)
    dt=0.1; % (seconds)
    THETA=missile(V_int,theta,dt);
    fprintf('Angle needed to travel 400 meters is %3.1f radians\n', THETA);
end

Then I have a function that calculates the distance travled over a range of angles to ensure that the projectile will be within range of the target

function [x,y]=projectile(V_int,theta,dt)
time = dt; %(seconds)
k = 0.32; %drag coefficient (given)
g = -9.81; %(m/s^2)
%First time step in x direction
x(1) = 0; %initial x position (meters)
v_int_x = V_int*cos(theta); %initial velocity in x direction (m/s)
a_x = -v_int_x*k; %initial acceleration in x direction (m/s^2)
x(2) = x(1)+v_int_x*time+0.5*a_x*(time^2); %second position in x direction (meters)
v_fin_x = v_int_x+a_x*time;  %(m/s)
%First time step in y direction
y(1) = 0; %initial y postision (meters)
v_int_y = V_int*sin(theta); %initial velocity in y direction (m/s)
a_y = g-v_int_y*k; %initial acceleration in y direction (m/s^2)
y(2)=y(1)+v_int_y*time+0.5*a_x*(time^2); %second y position (meters)
v_fin_y=v_int_y+a_y*time; %second velocity in y direction (m/s)
time=time+dt; %time step added to time already elapsed to give total time 
i=3; %counter
while y(i-1)>=0
    %calculates x values
    a_x=-v_fin_x*k; %acceleration in x direction for each time step (m/s^2)
    x(i)=x(i-1)+v_fin_x*time+0.5*a_x*(time^2); %x position for each time step (meters)
    v_fin_x=v_fin_x+a_x*time; %velocity in x direction for each time step (m/s)
    %calculates y values
    a_y=g-v_fin_y*k; %acceleration in y direction for each time step (m/s^2)
    y(i)=y(i-1)+v_fin_y*time+0.5*a_y*(time^2); %position in y direction for each time step (meters)
    v_fin_y=v_fin_y+a_y*time; %velocity in y direction for each time step (m/s)
    %change counter and timestep to continue loop
    i=i+1; %updates placement of next series of numbers for vectors
    time=time+dt; %updates total time elapsed (seconds)
end
end

And now I am trying to finish the function that will determine the angle needed for the given target

function THETA=missile(V_int,theta,dt) % Given initial velocity, theta, change in theta and a time step,
%  function will determine the change in horizontal distance. 
for theta=0:0.1:pi %(radians)
    x=projectile(V_int,theta,dt);
end

%determine the angle that will give the maximum distance travled
index=(find(x==max(x))); % Finds largest distance traveled fo all values theta
max_theta=theta(index); % Max theta used to go furthest distance
x_distance_1=max(abs(x)); % Max distance traveled
theta_1=max_theta; % Max theta will become first theta used 
dist_from_target=x_distance_1-target; % Determines how far from target the missile landed
theta=theta_1-0.1; %changes theta so function can be run again and we can determine change_in_theta
x=projectile(V_int,theta);
change_in_x=x-x_distance_1;
change_in_theta=(d_theta/change_in_x)*dist_from_target;
error=change_in_x;
   
while error>=2 || error<=-2 % Loop will run as long as the error is more that 2 meters in either direction
    x=projectile(V_int,theta,dt);
    dist_from_target=x-target;
    change_in_theta=(d_theta/change_in_x)*dist_from_target;
    theta=theta+change_in_theta;
    THETA=theta;
end

end

I am getting an error in line 12 of this last function,

dist_from_target=x_distance_1-target; % Determines how far from target the missile landed

I'm guessing it has something to do with the naming of the variable between the two functions? But I am not getting a reason for the error when it pops up in the command window.

[Rik]

Pasting this into an editor immediately gives me two m-lint warnings:

function THETA=missile(V_int,theta,dt)
%theta is unused
change_in_theta=(d_theta/change_in_x)*dist_from_target;
%the value assigned to this variable is unused

Then when I try to run it I get your error:

Undefined function or variable 'target'.

Error in Untitled>missile (line 50)
dist_from_target=x_distance_1-target; % Determines how far from target the missile landed

Error in Untitled (line 5)
    THETA=missile(V_int,theta,dt);

So you need to define the variable (or function) target and decide if those two warnings can be ignored, and if not, what you need to do to resolve them.

Answer 1

[Image Analyst]

You need to pass target into the function(s) that need it. Try this when you define the missile() function:

function THETA = missile(V_int, theta, dt, target)

Then when you call missile(), pass in target:

THETA = missile(V_int, theta, dt, target);