Make an array from function input and output

I have a function that inputs velocity and angle, and outputs the distance the ball travels. Function below:

function distance = DTask1_f (v, angle)
h = 1.5;
g = 9.8;

t = linspace (0,10,1000);

x=v*cos(angle*pi/180)*t;
y=h+v*sin(angle*pi/180)*t-0.5*g*t.^2;

ind = find (x == min(x(y<0)));
fprintf ('The ball hits the ground at a distance of %5.4f meters.', x(ind));
distance = x(ind);

end

I now need to write a script that uses the function, and while using a set value for velocity, will graph angle and distance over a set of angles. My script so far:

for angle = 10:13
    v  = 4;
    y = DTask1_f (v, angle);
    x = [angle];    

      a = [x;y]

end

figure
plot(x,y)
xlabel('Angle (deg)');
ylabel('Distance (m)');
title('Ball Trajectory');

I think I need to first make an array using the angle (input) and distance (output), and then graph the array, but im not sure how to make the array. At the moment, it only gives me the last two points.

Apologies if this is a simplistic question, but thanks for the help.

Answer 1

[Stephan]

Hi,

use:

angle_range = 10:1:13

for k = 1:length(angle_range)
      v = 4; 
      a(k,2) = DTask1_f (v, angle_range(k))
      a(k,1) = angle_range(k)
end

figure 
plot(a(:,1),a(:,2)) 
xlabel('Angle (deg)');
ylabel('Distance (m)');
title('Ball Trajectory');

If you want to extend or vary the range of angle or make other stepsize for angle modify first line.

Best regards

Stephan

[Corey Kovacs]

Hey, thanks that worked.

The last thing im trying to do, is display a different message if the ball is in the air for more than 10 seconds. I think i need to do this by editing the function, so i have tried to add in an if loop:

function distance = DTask1_f (v, angle)
h = 1.5;
g = 9.8;

t = linspace (0,10,50000);

x=v*cos(angle*pi/180)*t;
y=h+v*sin(angle*pi/180)*t-0.5*g*t.^2;

if t > 10
    fprintf ('Nan');
else ind = find (x == min(x(y<0)));
    fprintf ('The ball hits the ground at a distance of %5.4f meters.\n', x(ind));
    distance = x(ind);
end

end

This is my script, slightly edited the answer you provided:

angle = 0:60;

for k = 1:length(angle)
    v  = 60;

      a(k,2) = DTask1_f (v, angle(k));
      a(k,1) = angle(k);    

end

figure
plot(a(:,1),a(:,2))
xlabel('Angle (deg)');
ylabel('Distance (m)');
legend('v = 4 m/s')
title('Ball Trajectory');

Thank you

[Stephan]

Hi,

this part has a dynamic legend now for v - No need to write it by hand everytime it is changed:

angle = 0:60;

for k = 1:length(angle)
    v  = 60;
    a(k,2) = DTask1_f (v, angle(k));
    a(k,1) = angle(k);    
end

figure
plot(a(:,1),a(:,2))
xlabel('Angle (deg)');
ylabel('Distance (m)');
legend(['v = ', num2str(v), ' m/s'])
title('Ball Trajectory');

The function should now work as you wanted it to do, with some more informations when fprinf command gives output:

function distance = DTask1_f (v, angle)
h = 1.5;
g = 9.81;

t = linspace (0,15,50000);
x=v*cos(angle*pi/180)*t;
y=h+v*sin(angle*pi/180)*t-0.5*g*t.^2;

ind = find (x == min(x(y<0)));
distance = x(ind);

if t(ind) <= 10
    fprintf ('Angle: %1.0f Degrees - The ball hits the ground at a distance of %5.4f meters in %5.4f seconds. \n',angle, x(ind), t(ind));
else
    fprintf ('NaN - Angle: %1.0f Degrees - Time: %5.4f seconds \n', angle, t(ind));
end
end

Best regards

Stephan

[Corey Kovacs]

Thanks, that worked :)

Answer 2

[KSSV]

angle = 10:13 ;
x = angle ;
y = zeros(size(angle)) ;
for i = 1:length(angle)
    v  = 4;
    y(i) = DTask1_f (v, angle(i));        
end
figure
plot(x,y)
xlabel('Angle (deg)');
ylabel('Distance (m)');
title('Ball Trajectory');

[Corey Kovacs]

Your answer also worked, but i found the above answer easier to understand.

[Zach Russell]

5 years later...I found this answer to be easier to follow. Thanks for the help, if you are still out there.

[KSSV]

@Zach Russell yes I am here... :) you can acknowledge by voting the answer.