How to solve a plotting problem regarding straight lines

How can I make the two lines meet in their intersection point as shown in the figure below ?

(I want to obtain the two lines that I've drawn using red dots!)

clc ;clear all; close all; 
%Profilo
gamma = 1.4;

xdorso = [0 0.7 1]; xventre = [0 0.45 1];
ydorso = [0 0.03 0]; yventre = [0 -0.05 0];

delta1 = atand(0.03/0.44);
delta2 = atand(0.05/0.45);
delta3 = atand(0.03/0.56);
delta4 = atand(0.05/0.55);


n = 1000;
x = linspace(0,1,n);
alfa = -8:2:8;
deviazionedorso = delta1 + abs(alfa(1:4)); 
deviazioneventre = delta2 + alfa(5:end); 

mach1 = 1.01:0.001:1.6;
lunghezza = length(mach1);
massimo = mach1;
for i = 1:lunghezza
m1 = mach1(i);
epsmin = asin(1/m1)*57.3;
eps = linspace(epsmin,90,30);
delta = abaco(eps,m1,gamma);
massimo(i)= max(delta);
figure(1)
plot(eps,delta);
hold on
end

machcriticodorso = deviazionedorso;
for i = 1:length(deviazionedorso)
    calcolod = deviazionedorso(i);
for j = 1:lunghezza
    if abs(massimo(j)-calcolod)<0.1
        machcriticodorso(i) = mach1(j);
    end
    
end
end 

machcriticoventre = deviazioneventre;
for i = 1:length(deviazioneventre)
    calcolov = deviazioneventre(i);
for j = 1:lunghezza
    if abs(massimo(j)-calcolov)<0.1
    machcriticoventre(i) = mach1(j);
    end
    
end
end 

machcriticosuperiore = [machcriticodorso machcriticoventre];

 figure(4);
 plot(alfa,machcriticosuperiore,'k-o');
 xlabel('\alpha'); ylabel('M_{cr_{sup}}');
 axis([-8 8 1 1.6])

Answer 1

[Turlough Hughes]

We don't really need all that code to answer the question. It would be much more preferable to just post some sample data. Anyway, I've tried to replicate your data as follows:

x=linspace(-8,8,9);
y=[linspace(0.5,0.28,4) linspace(0.29,0.59,5)];

Where x and y correspond to the data in alfa,machcriticosuperiore.

You could use a linear fit to the "two lines" and then solve for the point of intersection as follows:

idx=x<=-1;
l1=polyfit(x(idx),y(idx),1); % l1 is coefficient m, c, of a linear fit to the data
l2=polyfit(x(~idx),y(~idx),1);
xi=(l2(2)-l1(2))/(l1(1)-l2(1)); % When y of line 1 = y of line 2, you get xi=(c2-c1)/(m1-m2)
yi=l1(1)*xi+l1(2);

plot(x,y,'ok')
hold on, plot(xi,yi,'or')

You could also insert the intersection point into your original data and then plot with the line:

x=[x(idx) xi x(~idx)];
y=[y(idx) yi y(~idx)];
xlabel('\alpha'); ylabel('M_{cr_{sup}}');
plot(x,y,'-ok');

[Giuseppe]

It works very well! Thank you, Thurlough Hughes!

Edit. The second part of your prompt (plotting with the intersection) seems to not work !

I obtain this:

Can you help me ?

EDIT: I've solved plotting two vectors of 10 elements by simply adding the extrapolated value!