# Help with plotting in matlab

• MATLAB
Okay so I am really new to matlab, I mean REALLY new. I am trying to write a program for one of my classes but I am having some trouble. I keep getting this error message:

??? Error using ==> plot
Invalid first data argument

Error in ==> guessTraj at 89
plot('b-')

And here is my code:

Code:
function [output]= guessTraj(target_dis)

target_dis=input('distance :');

error = sqrt(target_dis);

real = isreal(error);

if real == 0 & isnumeric(target)== 0

output = 4

disp('Invalid Distance')

end

angle = input('Please enter the angle in degrees:');

velocity = input('Please enter the velocity the ball is thrown:');

vel_error = sqrt(velocity);

vel_check = isreal(vel_error);

if vel_check == 0

disp('Invalid Velocity')

end

VY = velocity * sin(radians) ;

VX = velocity * cos(radians) ;

t = (2*velocity)/9.81 ;

x_dis = VX * t ;

y_dis = VY * t ;

H1 = target_dis + 2.5 ;

H2 = target_dis - 2.5 ;

x = 0:x_dis/50:x_dis;

plot(x,x_dis,target_dis,0,'mo')

xlabel ('Distance the ball Traveled')

ylabel ('Height of the ball')

legend ('Trajectory of Ball', 'Location', 'SouthEastOutside')

hold on

timeVector = 0:t/50:t;

plot('b-')

if x_dis <= H1 && x_dis >= H2

title('The ball hit the target')

output = 1;

disp('1. The ball hit the target!!!!!')

elseif x_dis < H1

title('The ball was underthrown')

under = target_dis-x_dis;

output = 2;

disp('2. The ball was underthrown')

elseif x_dis > H2

title('The ball was overthrown')

over = x_dis-target_dis;

output = 3;

disp('3. The ball was overthrown')

end

I'm not sure what I'm doing wrong. I want to plot the path of the object... What am I doing wrong?

Thanks so much!!
Code: