Why does plot function just draw points instead of line

Hi, I have a problem with plot function. It only draw points instead of line. LineWidth and putting '-' doesn't work.

    % for j=2:stc
    for i=2:n-1
        M(j,i)=K1*(M(j-1,i+1)-2*M(j-1,i)+M(j-1,i-1))+M(j-1,i);
        plot(j,M(j,i),'-','LineWidth',3)
        hold on
    end
    M(j,n)=-K3*(M(j,n-1)-To)+M(j,n-2)
    end

With this code I get plot like this:

Does anyone know what is wrong with code and how to get solid line back to plot? Thanks

[Christine Tobler]

I don't know what's happening. Does this still happen if you restart MATLAB and directly call

plot([1 2], [1 2], '-')

Answer 1

[Walter Roberson]

This is expected. One line is generated for each column of y values (or just one line if y is a row vector) for each call to plot(). You are making multiple calls to plot(), giving a single coordinate each time, so each one is generating a different line.

If you want to join together multiple points in a single line then all of the values must be passed to the plot() call. In practical terms this means you should move your plot() call to after the "for i" loop and plot(j, M(i,:)) . Or better yet move it to after the "for j" loop and plot(2:stc, M(2:end,:))

[martian]

Thanks for your answer. I moved plot after both loops and it works now :)