why is my loop printing 0 instead of a value, not sure which part of the code is incorrect

right now the code is at an increment of 15 to test, but the final incremment will be 0.01

code needs to have an if statement within the while loop.

%range is the maximum achievable horizontal distance
% range angle is the angle that yields the maximum horizontaal distance
%   use a whilel loop with a nested if statement to compute the maximum
%   landing distance (range) ange the angle corrsesponding to the maximum
%   landing distance (rangle angle) of the ME En 1010 ping pong cannon

function [range, rangeAngle] = ProjectileRange(d1, d2, v0)
thetaL = 90;
range = 0;
rangeAngle = 0;
[xLand] = LandingDistance(d1, d2, v0, thetaL);
while thetaL <= 90;
    if xLand > range
        range = xLand
        rangeAngle = thetaL
    end 
    thetaL = thetaL + 15;
end
end 
%% test
d1 = 0.0876;
d2 = 0.1190;
v0 = 3.2;
[range, rangeAngle] = ProjectileRange(d1, d2, v0);
fprintf('The range is %.2f m at a launch angle of %.2f degrees', range, rangeAngle)

this is what it prints:

The range is 0.00 m at a launch angle of 0.00 degrees>>

I need it to print "the range is 1.29 m at a launch angle of 41.6 degrees" when it has an incrememnt of 0.01

[Cris LaPierre]

Please share your LandingDistance function.

Initial guess is that your if statement code is not getting run, most likely because xLand <= range. We would need your function code to know for sure.

[ERIN]

I was calling Landingdistance before the loop and I needed to call it inside the loop

%% test
d1 = 0.0876;
d2 = 0.1190;
v0 = 3.2;
[range, rangeAngle] = ProjectileRange(d1, d2, v0);

Unrecognized function or variable 'Quadratic'.

Error in solution>LandingDistance (line 21)
[root] = Quadratic(a, b, c, plusOrMinus); % neg root

Error in solution>ProjectileRange (line 32)
[xLand] = LandingDistance(d1, d2, v0, thetaL);

fprintf('The range is %.2f m at a launch angle of %.2f degrees', range, rangeAngle)


% landing distance function
function [xLand] = LandingDistance(d1, d2, v0, thetaL)
% xLand --> the horizontal distance traveled by the projectile
v0x = v0 * cosd(thetaL);
v0y = v0 * sind(thetaL);
x0 = d2*cosd(thetaL);
y0 = d1 + d2*sind(thetaL);
g = 9.81; % gravitational acceleration in m/s^2
a = -0.5*g; % g = acceleration due to gravity in m/s^2
b = v0y; % initial velocity in y direction
c = y0; % initial y position
plusOrMinus = -1;
[root] = Quadratic(a, b, c, plusOrMinus); % neg root
tLand = root;
xLand = x0 + (v0x*tLand);
end


function [range, rangeAngle] = ProjectileRange(d1, d2, v0)
thetaL = 0;
range = 0;
rangeAngle = 0;
while (thetaL <= 90)
    [xLand] = LandingDistance(d1, d2, v0, thetaL);
    if (xLand > range)
        range = xLand;
        rangeAngle = thetaL;
    end 
    thetaL = thetaL + 0.01;
end
end 

[Walter Roberson]

plusOrMinus = -1;
[root] = Quadratic(a, b, c, plusOrMinus); % neg root

You ask for the negative root

xLand = x0 + (v0x*tLand);

x0 might not be enough to turn it positive

    [xLand] = LandingDistance(d1, d2, v0, thetaL);
    if (xLand > range)

xLand might be negative, and so will not be > 0

[Cris LaPierre]

Still can't run your code because the code for Quadratic is missing.

Answer 1

[charan]

Hello Erin,

For the function "LandingDistance" the inputs "d1","d2","v0" are fixed and "thetaL" can vary from 0 to 90. The following code shows the possible values of "xLand".

thetaL=0:1:90;
d1 = 0.0876;
d2 = 0.1190;
v0 = 3.2;
v0x = v0 * cosd(thetaL);
v0y = v0 * sind(thetaL);
x0 = d2*cosd(thetaL);
y0 = d1 + d2*sind(thetaL);
g = 9.81; % gravitational acceleration in m/s^2
a = -0.5*g; % g = acceleration due to gravity in m/s^2
b = v0y; % initial velocity in y direction
c = y0; % initial y position
plusOrMinus = -1;
[root] = roots([a, b, c]); % neg root
tLand = min(root);
xLand = x0 + (v0x*tLand);
plot(thetaL,xLand);

●

max(xLand)

ans = 0

As seen from the graph the value of "xLand" is always less than or equal to zero. The "range" variable was initialized to zero, so the "if" condition is never satisfied and the execution does not go into the "if" loop. Hence the value of "range" remains zero.