I want to add a 45-degree line on my plot. I tried some ways (including refline) all give me a 38-degree line!

Hey all

I wanted to have a 45-degree reference line on my plot. I searched and found there is a function namely refline so I use it but as you can see here it renders me a 38-degree line:

I even used

axis equal

but another problem appears. I mean although the line converted to 45 degrees but some space appears on my graph that is not good:

Here is the code that I used:

MONTHLY = scatter(X, Y)
refline
axis equal

As a result, I want something like a black line this graph:

In order to compare trendline (red line) with the perfect condition (45-degree black line).

I attach my X and Y.

Thank you so much

[Walter Roberson]

axis equal is right. You might need to use xlim() or ylim() afterwards

Answer 1

[Birdman]

Try the following:

figure(1);hold on;
MONTHLY=scatter(X,Y);
plot(0:600); %45 degree line
plot(0:600,0.73*(0:600)+6.47); %trend line
legend('X-Y Line','45 degree Line','Trend Line')

[BN]

Thank you,

May I ask you what is 0.73 and 6.47 and how you obtain them?

[Birdman]

Those values are in the figure that you shared above:

[BN]

Dear Birdman,

Thank you so much again. Why this method does not work well on my other X and Y points? I even use Walter Roberson xlim() and ylim() suggestion but the 45-degree line won't draw correct.

Look, I use this code:

clf
figure(1);
hold on;

class1 = scatter(X,Y,12,'k','filled');

[pp,s] = polyfit(X,Y,1);

r_squared = 1 - s.normr^2 / norm(Y-mean(Y))^2;

R2 = r_squared;

plot(1:max(X),pp(1)*(1:max(X))+pp(2)); %trend line

str = {sprintf('y = %.2fx+%.2f',pp(1),pp(2)),sprintf('R^2 = %.2f',r_squared)};

annotation('textbox', [0.2, 0.75, .1, .1], 'String',str ,'FitBoxToText',...
    'on','fontname','Cambria Math','HorizontalAlignment', 'center',...
    'FontSize',8,'BackgroundColor', 'white');

set(gca,'fontname','Times New Roman','FontSize',8)  % Set it to times

xlabel('Observed','FontSize',8)
ylabel('Modeled','FontSize',8)


box on;
grid on

plot(1:max(X),'k'); %45 degree line <<<<<<<<<<<<<<<<

xlim([0 max(X)])
ylim([0 max(Y)])

And here is the results:

Thanks.

Answer 2

[Ameer Hamza]

Explicitly specify slope with refline

MONTHLY = scatter(X, Y)
refline(1)
axis equal

Or draw both lines

MONTHLY = scatter(X, Y)
r1 = refline;
r1.LineWidth = 1;
r2 = refline(1);
r2.LineWidth = 1;
axis equal

[BN]

Thank you so much I tried this approach but I don't know why doesnt work dor me, Here is the results:

I even use xlim and ylim

xlim([0 max(X)])
ylim([0 max(Y)])

But not works.

Thank you.

Answer 3

[Kouadio Guillaume N'DRI]

In case someone still struggling with this. Find below my suggestion. I had the same problem with the refline.

x1=rand(1,50);
x2=rand(1,50);
scatter(x1,x2)
axis([0 max(max(x1),max(x2)) 0 max(max(x1),max(x2))])
hold on
plot([0 max(max(x1),max(x2))], [0 max(max(x1),max(x2))])