How to set multiple limits for multiple lines in a single graph with given data

I currently have a graph that has 2 sloped lines. I cannot simply set the boundaries of X because the data was given in matrix El. I want to have a line go from X = 9 to 13 and another line from X = 13 to 16. El is a matrix of 2x1601 (2 is for 2 lines) and I just want to keep the portion between those limits. Here is the code (may be a bit long)

I tried linspace so that I could even plot it, but I see now that it just squishes the values of El into the desired limits, giving me the wrong line.

I am trying to automatically create graphs (pourbaix diagrams) that can be pretty complex.

This is what I want:

This is what I'm getting:

Basically, the code is set up to calculate the slope of those 2 lines, where it will then calculate the intersection of them. This intersection is then set as a lower limit for the line that goes from 13 to 16 (the line with a higher slope). So I want the line with the lesser slope to be in the range of X = 9-13

%setting up sloped lines
s1a = El(1,:);
s2a = El(2,:);
ab1 = linspace(b,a,length(s1a));
ab2 = linspace(a,mx,length(s2a));

s1 = diff(s1a)/diff(ab1)
s2 = diff(s2a)/diff(ab1)

%finding intersection of the 2 lines so boundary can be found for vert line   
[x1,y1] = polyxpoly(pH,s1a,pH,s2a);

    if s1 > s2
        plot(ab2,s1a);
        plot(ab1,s2a);
    else 
        plot(ab1,s1a);
        plot(ab2,s2a);
    end

[darova]

Do you have a picture?

[Austin Hernandez]

Yes, the first is what I want:

and as you can see, the lines are "squished"

[darova]

Can you attach the data?

[Austin Hernandez]

I'm not sure if I can do that, when I say the data is given, I mean that the values were previously calculated in a loop that was then stored into the 2x1601 matrix called El, which is what I'm trying to plot. This is the overall code the calcs are in a for loop and then stored into El:

El was preallocated.

El = ones(1,1601);
cc = 1;
cb = 1;
cc = 1;
pH = 0:0.01:16
E = -2:0.01:2
for %(this loop will store the data into matrix El when the else statement is triggered)
    (some calculations and user inputs)
    
%calculations for vertical, horizontal, or sloped lines
    if  n == 0
        pH0 = -g01/(C*m);  %pH0 for the rxn, which is independent of charge
        C1 = 1/m *(logk);  %constant of ions and logK
        pHa(ca,:) = pH0 - C1;    %value that needs to be recorded
        plot(pHa(ca,:)*ones(size(E)),E,'LineWidth',2); %since pH is constant, we must expand pH to have the same size as E
        ca = ca + 1;
    elseif m == 0 
        Eh1(cb,:) = E0 + (CF/n)*logk;
        plot(pH, Eh1(cb,:)*ones(size(pH)),'LineWidth',2);
        cb = cb + 1;
    else 
        C2 = E0 - CF/n*logk;
        El(cc,:) = -m/n*CF*pH + C2;
        plot(pH, El(cc,:),'LineWidth',2);  
        cc = cc + 1;
    end  
    
    %at the end of the loop, the program will then attempt to construct 
    %boundaries
end

%The basic outline of the graph is generated, where the automatically
%constructed graph should form
hold off
figure
plot(pH,h,'k--', pH, o ,'k--');
axis([0 16 -2 2]);
xlabel('pH');
ylabel('E (V)');
hold on

%the recorded arrays will then be used to find the boundaries of the graphs
%and it should automatically generate these no matter the order of inputted
%equations


%setting up the horizontal line
a = max(pHa);   %the max pH will act as a starting point for the line with the highest slope
b = min(pHa);   %starting point of line with lower slope
mx = 16;        %graph max window
u = 0:0.01:b;   %range for horizonatal line
bo = a:0.01:16; %range for last domain
yb = Eh1*ones(size(u)); %making u,yb plottable 
plot(u,yb);

%setting up sloped lines
p = b:0.01:a;   %boundaries for lesser sloped lines
s1a = El(1,:);  %the 1st row of the lines
s2a = El(2,:);  %2nd row
ab1 = linspace(b,a,length(s1a));    %attempt to match sizes of data, doesn't work
ab2 = linspace(a,mx,length(s2a));

%slopes of inputted lines
s1 = diff(s1a)/diff(ab1);
s2 = diff(s2a)/diff(ab1);

%finding intersection of the 2 lines so boundary can be found for vert line   
[x1,y1] = polyxpoly(pH,s1a,pH,s2a);

%this statement will check the slopes of the lines and determine what
%domain it should fall under (ranges of pH)
if s1 > s2
        plot(ab2,s1a,'LineWidth',2); %if slope1 > slope2, then slope 1 will be placed in the outer region
        plot(ab1,s2a,'LineWidth',2);
else 
        plot(ab1,s1a,'LineWidth',2);
        plot(ab2,s2a,'LineWidth',2);
end

[darova]

Im completely lost. There is too much information for me. Can you simplify the question? Maybe another picture?

[Austin Hernandez]

The program I'm writing will automatically construct 2 graphs. Heres' the first:

The second is the "polished" version of the first graph, which is automatically found after determining where the line stops. I want a rough version of this:

but instead I get this:

The first graph is made from user inputs, and the second is an attempt at getting the proper graphs. I just simply want to take the data from the for loop, and plot it so that it looks like the 2nd picture. But I don't know how to automatically set the limits of the lines from the calculated data.