legend not showing proper titles for the legend just stuck on one

clear

clc

data = xlsread('something.xlsx');

x = data(:,1);

y = data(:,2);

n = length(x);

sum_x = sum(x);

sum_y = sum(y);

sum_xy = sum(x.*y);

sum_x2 = sum(x.^2);

a1 = (n*sum_xy - sum_x*sum_y) / (n*sum_x2 -sum_x^2)

a0 = (sum_y/n) - (a1 * sum_x/n)

str = ['The line of best fit that fits your data is y = ',...

num2str(a1),'x + ',num2str(a0),...

'. Please enter value of x for which you would like a value of y computed.'];

new_x = inputdlg(str);

new_x = str2num(new_x{1});

new_y = a1*new_x + a0;

disp(['The value of y, as predicted by the line of best fit, for the value of x you provided, is ',num2str(new_y)]);

plot(x,a1,'ob',x,a0,'gs',x,new_y,'pr')

xlabel('x value')

ylabel('y value')

title('linear regression')

grid on

axis([0 100 -1 50])

pause(1);

legend('slope','y-int','new value','Location','Southwest')

hold on

[Adam Danz]

Could it be that your a1, a0, or new_y values are empty or filled with NaNs?

When I supply your code with values, the legend appears as expected (see below).

plot(1:10,1:10,'ob',1:10,(1:10).*2,'gs',1:10,(1:10).*3,'pr')
xlabel('x value')
ylabel('y value')
title('linear regression')
grid on
legend('slope','y-int','new value','Location','Southwest')

Answer 1

[Ganesh Regoti]

Hey Christopher,

From your question, I understand that the legend is not reciprocating appropriate markers. Since you are trying to plot a vector against an integer in the same figure, using the legend command is resulting in incorrect results. To resolve this issue, consider using a vector of same integer instead –

a1 = a1.*ones(length(x),1);
a0 = a0.*ones(length(x),1);
new_y = new_y.*ones(length(x),1);
 
plot(x,a1,'ob',x,a0,'gs',x,new_y,'pr'); 

Now, when you run the following command, you will get the appropriate results

legend({'slope','y-int','new value'},'Location','southwest');