How to find points between two intersecting lines?

I have two straight lines defined by equations (say) x+y=3 and 2x-3y=4. I have to find out the points which lies between these two lines in the xy plot as in the attached figure. Can anyone suggest me how can i find the points between two lines in a plot?

Thank You

[Image Analyst]

Those lines are not on your graph.

[Niraj Bal Tamang]

Sorry. I just gave a random equations of straight line for assumption. I am attaching the whole code and variables if you want to give it a try. I am trying to get the points between each of those lines for classification.

scatter(usarea,slope);
    set(gca,'xscale','log','yscale','log');
    xlabel('Upstream Drainage Area (sq km)');
    ylabel('Slope (m/m)');
    hold on
    xline(7*10^5,'Color','r','LineStyle','--');%vertical line
    hold on
    plot([1.1*10^6 10^10],[0.15 0.15],'--r');%horizontal line
    hold on
    plot([7*10^5 5*10^9],[0.2 10^-4],'--r');%diagonal line
    hold off
    grid on

Answer 1

[G A]

myData = [X,Y];
y1 = 3 - X;
y2 = 2/3*X + 4/3;
Y1 = Y(Y < y2 & Y > y1);
X1 = X(Y < y2 & Y > y1); % or X1 = X(Y == Y1)
myData1 = [X1,Y1];

[Niraj Bal Tamang]

Is this applicable for the scatterplot also? I want to define lines in the plot and categorize the points between those lines.

scatter(usarea,slope);
    set(gca,'xscale','log','yscale','log');
    xlabel('Upstream Drainage Area (sq km)');
    ylabel('Slope (m/m)');
    hold on
    xline(7*10^5,'Color','r','LineStyle','--');%vertical line
    hold on
    plot([1.1*10^6 10^10],[0.15 0.15],'--r');%horizontal line
    hold on
    plot([7*10^5 5*10^9],[0.2 10^-4],'--r');%diagonal line
    hold off
    grid on

[G A]

It does not matter how are you are plotting your X-Y data. If your data are defined by X and Y arrays of the same length (myData), then you can use the method I have shown to get the data between lines given by [X,y1] and [X,y2]. Those data are defined as myData1=[X1,Y1], again, lengths of X1 and Y1 are equal. And these data ([X,Y] and [X1,Y1] or [X,y1] and [X,y2]) you can plot in any way you wish.

[G A]

load('H_usarea_and_slope.mat',"usarea","slope")

scatter(usarea,slope);
    set(gca,'xscale','log','yscale','log');
    xlabel('Upstream Drainage Area (sq km)');
    ylabel('Slope (m/m)');
    hold on
    xline(7*10^5,'Color','r','LineStyle','--');%vertical line
    hold on
    plot([1.1*10^6 10^10],[0.15 0.15],'--r');%horizontal line
    hold on
    plot([7*10^5 5*10^9],[0.2 10^-4],'--r');%diagonal line
    
    grid on
    
    X=usarea;
    Y=slope;
    
    Y1=ones(size(X))*0.15; % horizontal line
    B=1e7; % vertical line, I shifted it to the right for demonstration purpose
    % defining diagonal line as log(y)=a*log(x)+b
    x1=log(7e5);
    x2=log(5e9);
    y1=log(0.2);
    y2=log(1e-4);
    a=(y2-y1)/(x2-x1);
    b=y1-a*x1;
    
    Y2=exp(a*log(X)+b); % diagonal line
    
Y3 = Y(Y < Y1 & Y > Y2 & X > B); % Y-data between lines
X3 = X(Y < Y1 & Y > Y2 & X> B); % X-array

plot(X3,Y3,'.r');
plot(X,Y1,'--b');
plot(X,Y2,'--g');
xline(B,'--m');
hold off

[Niraj Bal Tamang]

Thank you so much.It's working now.