My graph is blank

ive written a code and the numbers on the x and y axis show up but im not getting any actual plots.

w = input('Enter weight "W" of aircraft value(kg)');
c_d0 = input('Enter profile drag coefficient "C_d0" of aircraft value');
s = input('Enter wing span "S" of aircraft value(m)');
p_0 = input('Enter initial power at sea level "P_0" of aircraft engine value(W)');
k = input('Enter induced drag coefficient "K" of aircraft value');

rho_0 = 1.225;
h=0:0.1:20;

for i=1:length(h)
    
    sigma(i)=20-h(i)/20+h(i);
    
    a=c_d0*0.5*rho_0*s;
    b=-p_0;
    c=k*w^2/0.5*rho_0*sigma(i).^2*s;
    
    y=[a 0 0 b c];
    r=roots(y);
end

    plot(r(3),h,r(4),h)

[KSSV]

h happens to be a vector, and r(3) , r(4) are scalars......you cannot plot like that.

[Adeola Badejo]

i see so how would you suggest i fix it?

Answer 1

[KSSV]

w = input('Enter weight "W" of aircraft value(kg)');
c_d0 = input('Enter profile drag coefficient "C_d0" of aircraft value');
s = input('Enter wing span "S" of aircraft value(m)');
p_0 = input('Enter initial power at sea level "P_0" of aircraft engine value(W)');
k = input('Enter induced drag coefficient "K" of aircraft value');

rho_0 = 1.225;
h=0:0.1:20;
r3 = zeros(size(h)) ;
r4 = zeros(size(h)) ; 
for i=1:length(h)
    
    sigma(i)=20-h(i)/20+h(i);
    
    a=c_d0*0.5*rho_0*s;
    b=-p_0;
    c=k*w^2/0.5*rho_0*sigma(i).^2*s;
    
    y=[a 0 0 b c];
    r=roots(y);
    r3(i) = y(3) ; 
    r4(i) = y(4) ; 
end

    plot(r3,h,r4,h)

[Adeola Badejo]

it plots now thank you i just dont think it plots the right answer

[KSSV]

The asked question purpose is solved. The right answer depends on what the problem is.

[Adeola Badejo]

the problem is to plot a graph of the minimum and maximum roots against h whichould give me a parabola but instead gives me a straight line so i must have gone wrong somewhere

[KSSV]

You can get min and max using:

r3(i) = min(y) ;
r4(i) = max(y) ; 

You need to rethink on your code.