Legend and graph doesn't have the same color

I have a problem with the color in the legend. I'm using a package "RF Utilities V1.2" which I found at http://www.mathworks.com/matlabcentral/fileexchange/22996-rf-utilities-v1-2. I'm using the function citi2s from that package to import data from citi-files.

I have a pretty long script where I have a lot of functions, I just made a shorter version which will work to state the problem here. For instance I have only two lines to plot, which is easy to do without a for-loop. In my original script I have the number of plots will be determined by the number of files the user selects, and therefore I need the for loop. I also need to use hold all to change the color every time.

This is my code:

   clear all;  

   pathname=char(strcat(pwd,'\')) 
   files = cell(1,2);
   files{1,1}=['DATA01.D1'];
   files{1,2}=['DATA02.D1'];

   number_of_selected_files=length(files);
   number_of_measurement_points=201;

   %Pre-allocate empty matrices:
   S_parameter_matrix=zeros(number_of_selected_files, 4,...
       number_of_measurement_points(1));
   freq=zeros(number_of_selected_files, number_of_measurement_points);
   filename=zeros(number_of_selected_files,1);

   %%----------------------- THIS WAY WORKS ---------------------
   load('S21.mat')
   number_of_selected_files=2;
   freq=linspace(1,1.1,201)*10^9;

   %%----------------- THIS WAY DOES NOT WORK -------------------
   %{ 
   for k=1:number_of_selected_files;
    [S_parameter_matrix(k,1,:), S_parameter_matrix(k,2,:), ...
        S_parameter_matrix(k,3,:), S_parameter_matrix(k,4,:), ...
        freq(k,:)]=citi2s(char(strcat(pathname, files(k))));
    end
   freq=freq/(1e-6); % GHz

   S21=squeeze(S_parameter_matrix(:,3,:));
   %}

   %%---------------------- REST OF SCRIPT ----------------------
   IL=-20*log10(abs(S21)); %Insertion loss
   fig1=figure;
   hold all
   for k=1:number_of_selected_files
    [~, name, ext]=fileparts(files{k}); 
   %Create filename-vector without file extension
    filename_string{k} = [char(name)]; 
       %Create string-vector with information for legend
    legend_string{k}=['Cable ' num2str(k) ': ' char(name)];
    plot(freq, IL(k,:))   
    end
    hold off
    leg=legend(legend_string, 'location', 'SouthOutside',....
    'Interpreter', 'none');

My problem is that if I use the citi2s-function to import the data my plot uses a different colororder than my legend does. The legend follows the default color order but the plot doesn't. It looks like this:

If I just load the data from the S21.mat-file the color is fine, like this:

Does anyone know why the way of importing the data can affect the color-order in the plot? Or a way to fix it? I'm attaching a zip-file with the script, citi2s, data-files and the S21.mat

Thank you in advance

[dpb]

What's the hold all there for before you've done anything to hold? We demonstrated in an earlier thread just this past week that setting hold state before an initial plot tends to muck things up. Remove it.

I believe then the primary problem w/ legend and colors is that you've then called hold off that resets the color order before legend. Remove it, too...

Then, legend should track the line patterns automagically. You can always ensure you're addressing the desired lines by saving and using the line handles and the optional handles array in legend but for simple case such as this shouldn't be necessary but it would look something like

hL=zeros(N,1);  % N is loop max
for k=1:N
  hL(k)=plot(freq, IL(k,:));  % save line handle
end
hLeg=legend(hL,legend_string, ...

[Björn]

Thanks. It's solved now but I appreciate the headsup with hold all. I have always used it like this

plot(x,y); hold all

Without hold off. But now when I had this problem I googled a lot for hold all and found many examples where they did like this. So this is the first time I wrote it like this, and thanks to your comment it's also the last :-).

[aerothermal]

Nice work!

Answer 1

[Geoff Hayes]

Björn - I was able to reproduce the problem with your code (very helpful to post all that). The problem occurs during the plotting, at the line of code

 plot(freq, IL(k,:))

IL is a 2x201 matrix, which is fine since k varies from 1 to 2. But, freq is a 2x201 matrix as well! So we are actually plotting the same data twice, and so are using four of the colours (as the second plot from each iteration just overlays the previous one).

Just replace the above line with

 plot(freq(k,:), IL(k,:));

and it should work fine.

[Björn]

Nice catch. Thank you very much!

It's pretty obvious now when you've pointed it out :-)

Answer 2

[Chad Greene]

You can link labels directly to their data with label. Labels take on the color of the data by default.

[Björn]

Thank's for the tip! I will check it out.