Question

I wonder why these two code doesn’t produce the same plot?

code 1:

x=[2,5,7];
y=[10,4,3];
plot(x,y);

code 2:

x=[2,5,7];
y=[10,4,3];

for i=1:length(x)
    xx=x(i);
    yy=y(i);
    plot(xx,yy);

end

EDITED:
How I can make the output of Code 2 similar to output in Code 1

Answer 1

Code 1

You’re drawing a line with the x and y coordinates defined in the vectors with the plot(x,y) command. By default, it means plot(x,y,'-'); which means you draw a line (-).

Code 2

You’re drawing individual points (no line) stored in the vectors since you’re calling plot for each point (xx,yy)

You can duplicate the effect in Code 2 in Code 1, with the following change:

plot(x,y,'.');

This forces MATLAB to only plot the points and not the connecting line

If you want the points and the line,

plot(x,y,'-.');

For more details, check out the documentation of the plot command.

Sample Code:

%# If you know the number of elements, preallocate
%# else just initialize xx = []; and yy =[];
xx = zeros(100,1);
yy = zeros(100,1);

%# Get the data
for i = 1:length(xx)
    xx(i) = getXSomehow();
    yy(i) = getYSomehow();
end

%# Plot the data
plot(xx,yy);