How can I fill area above a plot?

Hello, I am trying to fill the area above a curve in my top subplot. I have already filled the area beneath my lower curve but cannot seem to get the area above the upper curve. Both curves are create from sets of data points.

ax1 = subplot(2,1,1);
plot(Freq1,Gain_Upper)
hold on
basevalue = -15;
ar=area(Freq2,Gain_Lower,basevalue);

Answer 1

[Star Strider]

Try this:

x = 0:10:90;                                                    % Create Data
G1 = [-1 -2 -3 -4 -5 -7 -9 -11 -12 -13];                        % Create Data
G2 = [1 1 2 2 2 2 2 2 2 2];                                     % Create Data


figure
plot(x, G2)
axis([0 100    -15 5])
hold on
plot(x, G1)
patch([x fliplr(x)], [G1 min(ylim)*ones(size(G1))], 'r')        % Below Lower Curve
patch([x fliplr(x)], [G2 max(ylim)*ones(size(G2))], 'r')        % Above Upper Curve
hold off
grid

Experiment to get the result you want.

[Carly Beck]

I was able to re-create your answer with my data but when I add more data and seperate them into subplots the fill gets confused. Do I need to change the patch limits?

figure(4)
% top subplot
ax1 = subplot(2,1,1);
% Gain Plot Values
     Freq1 = [1;10;20;100];  % x2
Gain_Upper = [1;1;2;2];      % G2
     Freq2 = [1;50;100];     % x1
Gain_Lower = [-1;-3;-12];    % G1

plot(Freq1,Gain_Upper)
axis([0 100 -15 5])
hold on
plot(Freq2,Gain_Lower)
patch([Freq1 fliplr(Freq1)], [Gain_Upper max(ylim)*ones(size(Gain_Upper))], 'b') % Above Upper Curve
patch([Freq2 fliplr(Freq2)], [Gain_Lower min(ylim)*ones(size(Gain_Lower))], 'r') % Below Lower Curve
hold off
grid
title('Frequency Response Requirement')
xlabel('Frequency [Hz]')
ylabel('Gain [dB]')

% bottom subplot
ax2 = subplot(2,1,2);
% Phase Plot Values
Freq3 = [1;10;40;70;100];
Phase = [-5;-20;-70;-135;-180];
basevalue3 = -200;
area(Freq3,Phase,basevalue3)
axis([0 105 -200 0])
grid on 
xlabel('Frequency [Hz]')
ylabel('Phase(deg)')

[Star Strider]

The problem is simply that my original code uses row vectors, and your data are column vectors. The MATLAB plotting functions treat them differently.

The easiest way to fix that is to transpose your vectors in the patch calls:

patch([Freq1' fliplr(Freq1')], [Gain_Upper' max(ylim)*ones(size(Gain_Upper'))], 'b') % Above Upper Curve
patch([Freq2' fliplr(Freq2')], [Gain_Lower' min(ylim)*ones(size(Gain_Lower'))], 'r') % Below Lower Curve

producing this plot:

Note the use of the transpose operator ('). (The transpose operator has two forms, the complex-conjugate transpose (') and the simple transpose (.'). Your data are real, so there is no difference. I use (') here for convenience.)

[Carly Beck]

Oh okay, I got it now. Thank you!!

[Star Strider]

As always, my pleasure!

Answer 2

[Adam Danz]

Here you go (applied to fake data); let me know if you have any questions.

% Create fake data
Freq1 = 1:100; 
Gain_Upper = linspace(0,-200,numel(Freq1))+rand(size(Freq1))*10; 

% plot
figure
ax1 = axes; 
plot(ax1,Freq1,Gain_Upper, 'k-','LineWidth',3)

% Form polygon
ceiling = max(ylim(ax1));  %define top of polygon as top of y axis
xp = [Freq1,fliplr(Freq1)]; 
yp = [Gain_Upper, repmat(ceiling,size(Freq1))]; 
hold(ax1, 'on')

% Fill area above curve
fill(ax1,xp,yp,'g')

More info on fill(): https://www.mathworks.com/help/matlab/ref/fill.html

If you'd like to fill the area between two lines use this line instead:

yp = [Gain_Upper, UpperLineValues]; 
% Where UpperLineValues contain the y coordinates of the upper line