Find the intersection of two lines with multiple intersections.

Hi,

I am trying to find the intersection of these two lines and plot both. I have tried fzero() and fiind(), but they are both not working.

% Basic Variables
k_prime = 1000; np = .85; P = 750; rho = 1.225; S = 25; W = 1600*25; Cl_max = 1.5; k = .05;
Cdo = .025; Cd = Cdo + .05*(Cl_max^2); W_S = 1600; V = 0:200;
% Equations
Pa = k_prime * np * P;
Pr = (.5 * rho * S * Cdo * V.^3) + ((2*k*W^2)./(rho*S*V));
% Plotting
figure; ylim([0 10*10^5]); yline(Pa); hold on;
plot(V,Pr,'--'); hold on; legend("Available Power", "Required Power");

[Ankit]

Try this file from file exchange: Intersection of Two Lines (line_intersection) - File Exchange - MATLAB Central (mathworks.com)

Answer 1

[KSSV]

You may use this: https://in.mathworks.com/matlabcentral/fileexchange/22441-curve-intersections

% Basic Variables
k_prime = 1000; np = .85; P = 750; rho = 1.225; S = 25; W = 1600*25; Cl_max = 1.5; k = .05;
Cdo = .025; Cd = Cdo + .05*(Cl_max^2); W_S = 1600; V = 0:200;
% Equations
Pa = k_prime * np * P;
Pr = (.5 * rho * S * Cdo * V.^3) + ((2*k*W^2)./(rho*S*V));
% Plotting
figure; 
ylim([0 10*10^5]); 
yline(Pa); hold on;
plot(V,Pr,'--'); 
legend("Available Power", "Required Power");

% Find intersection
x = linspace(min(V),max(V),200) ;
y = Pa*ones(size(x)) ; 

P = InterX([x;y],[V;Pr]) ;

plot(P(1,:),P(2,:),'*r')

Answer 2

[Bruno Luong]

% Basic Variables
k_prime = 1000; np = .85; P = 750; rho = 1.225; S = 25; W = 1600*25; Cl_max = 1.5; k = .05;
Cdo = .025; Cd = Cdo + .05*(Cl_max^2); W_S = 1600; V = 0:200;
% Equations
Pa = k_prime * np * P;
Pr = (.5 * rho * S * Cdo * V.^3) + ((2*k*W^2)./(rho*S*V));
% Plotting
figure; ylim([0 10*10^5]); yline(Pa); hold on;
plot(V,Pr,'--'); hold on; legend("Available Power", "Required Power");

fun=@(V)(.5 * rho * S * Cdo * V.^3) + ((2*k*W^2)./(rho*S*V))-Pa;
V1=fzero(fun,20)

V1 = 8.1980

V2=fzero(fun,120)

V2 = 115.6625

plot([V1 V2],[Pa Pa],'or')