Plot array of x ,y both in 2 columns, got unexpected multiple line result.

Hi, :

I beg your pardon, I got some unexpected result of plot number of line. I have uploaded the .mat files which contained the x,y axes data.

The code is as below:

% plot_array_result_in_multiple_line.m
load('X.mat','X');
load('Y.mat','Y');


plot(log10(X(:,1)),20*log10(hypot(Y(:,1),Y(:,2))));
title( ['Plot Bode']);
xlabel( 'x=Freq-axis (in 10^n)') , ylabel( 'y=data value-axis (in dB)' );    
grid on;

But I get 3 lines on the plot figure, as I expect to be only one. One is possible because of the hypot(), root of square , but there is another one (the lowest one) I thought it's very strange, its y-values seems same as reciprocal of x-values, Can anyone know why does it plot this ? And how to fix it ?

Thank you very much.

Answer 1

[Alex Mcaulley]

Just one line is ploted. See this:

% plot_array_result_in_multiple_line.m
load('X.mat','X');
load('Y.mat','Y');
h = plot(log10(X(:,1)),20*log10(hypot(Y(:,1),Y(:,2))));
title( ['Plot Bode']);
xlabel( 'x=Freq-axis (in 10^n)') , ylabel( 'y=data value-axis (in dB)' );    
grid on;
findobj(h)
ans = 

  Line with properties:

              Color: [0 0.4470 0.7410]
          LineStyle: '-'
          LineWidth: 0.5000
             Marker: 'none'
         MarkerSize: 6
    MarkerFaceColor: 'none'
              XData: [1×3505 double]
              YData: [1×3505 double]
              ZData: [1×0 double]

  Show all properties
  

The problem is that you have repeated X(1) values (i.e. X(371) == X(1773)), but the corresponding Y are different. For that reason you get "unexpected results".

[Tamura Kentai]

Hi, Alex:

Thank you. Sorry for careless, I found there are five segments repeat the x-axis data.

If apply the following code, change the segment, it will show the different line of '5'.

About the 'segment = 1', the peak value is very low -20dB. <== I need to check this.

Best regards.

% plot_array_result_in_multiple_line.m
load('X.mat','X');
load('Y.mat','Y');

% there are 5 segments, repeat the x-axis in the data
segment = 5;

plot(log10(X(1+701*(segment-1):701*(segment-1+1),1)),20*log10(hypot(Y(1+701*(segment-1):701*(segment-1+1),1),Y(1+701*(segment-1):701*(segment-1+1),2))));
title( ['Plot Bode']);
xlabel( 'x=Freq-axis (in 10^n)') , ylabel( 'y=data value-axis (in dB)' );    
grid on;

[Tamura Kentai]

Hi, Alex:

May I ask, how to show the following of the 'line'.

My findobj(h) , return only a number '174.0449'

Thank you.

  Line with properties:
              Color: [0 0.4470 0.7410]
          LineStyle: '-'
          LineWidth: 0.5000
             Marker: 'none'
         MarkerSize: 6
    MarkerFaceColor: 'none'
              XData: [1×3505 double]
              YData: [1×3505 double]
              ZData: [1×0 double]
  Show all properties

[Alex Mcaulley]

Have you defined h?

h = plot(log10(X(1+701*(segment-1):701*(segment-1+1),1)),20*log10(hypot(Y(1+701*(segment-1):701*(segment-1+1),1),Y(1+701*(segment-1):701*(segment-1+1),2))));

[Tamura Kentai]

Hi, Alex:

Yes ,I tried it again, but only return a number '175.0450'.

Does it need only 'findobj(h)' ?

Thank you

[Alex Mcaulley]

Yes, it should work. Try with this (keeping the figure opened):

findobj(gcf,'type','line')

[Tamura Kentai]

Hi, Alex:

Yes, I tried, it returned different floating value.

thank you

>> findobj(gcf,'type','line')

ans =

175.0499

[Alex Mcaulley]

Sorry, but I don't know what is happening... Just a last try, what is the result of

findobj(gcf)
findall(gcf)

[Tamura Kentai]

Hi, Alex:

The returned value is as below, all is numbers.

Thank you.

>> findobj(gcf)

ans =

    1.0000
  175.0510
  176.0481

>> findall(gcf)

ans =

    1.0000
  175.0510
  146.0461
  134.0461
  133.0461
   82.0461
   66.0461
   59.0461
   39.0461
   20.0461
    2.0468
  179.0450
  178.0461
  177.0461
  176.0481
  174.0466
  173.0461
  172.0461
  171.0461
  170.0461
  167.0461
  166.0461
  165.0461
  151.0461
  150.0461
  149.0461
  148.0461
  147.0461
  145.0461
  144.0461
  143.0461
  142.0461
  141.0461
  140.0461
  139.0461
  138.0461
  137.0461
  136.0461
  135.0461
  132.0461
  131.0461
  122.0461
  113.0461
  106.0461
  105.0461
  104.0461
  103.0461
  102.0461
  101.0461
   92.0461
   91.0461
   90.0461
   89.0461
   88.0461
   87.0461
   86.0461
   85.0461
   84.0461
   83.0461
   81.0461
   80.0461
   79.0461
   78.0461
   77.0461
   76.0461
   75.0461
   74.0461
   73.0461
   72.0461
   71.0461
   70.0461
   69.0461
   68.0461
   67.0461
   65.0461
   64.0461
   63.0461
   62.0461
   61.0461
   60.0461
   58.0461
   57.0461
   56.0461
   55.0461
   54.0461
   53.0461
   52.0461
   51.0461
   50.0461
   49.0461
   48.0461
   47.0461
   46.0461
   45.0461
   44.0461
   43.0461
   42.0461
   41.0461
   40.0461
   38.0461
   37.0461
   36.0461
   35.0461
   34.0461
   33.0461
   32.0461
   31.0461
   30.0461
   29.0461
   28.0461
   27.0461
   21.0461
   19.0461
   18.0461
   17.0461
   16.0461
   15.0461
   13.0461
   12.0461
   11.0461
   10.0461
    9.0461
    8.0461
    7.0461
    6.0461
    5.0461
    4.0461
    3.0461
  169.0461
  168.0461
  164.0461
  163.0461
  162.0461
  161.0461
  160.0461
  159.0461
  158.0461
  157.0461
  156.0461
  155.0461
  154.0461
  153.0461
  152.0461
  130.0461
  129.0461
  128.0461
  127.0461
  126.0461
  123.0461
  121.0461
  120.0461
  119.0461
  118.0461
  117.0461
  116.0461
  115.0461
  114.0461
  112.0461
  111.0461
  110.0461
  109.0461
  108.0461
  107.0461
  100.0461
   99.0461
   98.0461
   97.0461
   96.0461
   95.0461
   94.0461
   93.0461
   26.0461
   25.0461
   24.0461
   23.0461
   22.0461
   14.0461
  125.0461
  124.0461

Answer 2

[Tamura Kentai]

Hi, :

I guess , get(h) will help to show more...under the 'figure 1' still opened.

>> get(h)
           DisplayName: ''
            Annotation: [1x1 hg.Annotation]
                 Color: [0 0 1]
             LineStyle: '-'
             LineWidth: 0.5000
                Marker: 'none'
            MarkerSize: 6
       MarkerEdgeColor: 'auto'
       MarkerFaceColor: 'none'
                 XData: [1x701 double]
                 YData: [1x701 double]
                 ZData: [1x0 double]
          BeingDeleted: 'off'
         ButtonDownFcn: []
              Children: [0x1 double]
              Clipping: 'on'
             CreateFcn: []
             DeleteFcn: []
            BusyAction: 'queue'
      HandleVisibility: 'on'
               HitTest: 'on'
         Interruptible: 'on'
              Selected: 'off'
    SelectionHighlight: 'on'
                   Tag: ''
                  Type: 'line'
         UIContextMenu: []
              UserData: []
               Visible: 'on'
                Parent: 173.0046
             XDataMode: 'manual'
           XDataSource: ''
           YDataSource: ''
           ZDataSource: ''