How to color or patch the region between a curve and the x axis

My code plots two curves. I want to color or in other words patch the region between the curves and the x-axis from 3-5 um. I am not sure how to properly define the y patch so my patch doesn't fill up the correct region of interest. Any form of help would be appreciated. Thank you.

clc;
close all;
c=3*10^8; % speed of light in vaccum
h=6.626*10.^-34; %  Planck constant 
k=1.38*10.^-23; %   Boltzmann constant
T=[700 900]; % Temperatures in Kelvin
Lam=(0.0:0.01:50)*1e-6; % in meters
figure(1)
for i=1:2
    A2(:,i)=(2*pi*h*c*c)./((Lam.^5).*(exp((h.*c)./(k.*T(i).*Lam))-1));
    hold on
    plot(Lam*1e6,A2(:,i)*1e-10,'r','linewidth',2) 
    x = [3 5];    % Define x  For patch
    y = [0.152 0.19]; % Define y For patch 
    patch([x fliplr(x)], [zeros(size(y)) fliplr(y)], 'b')
    hold off
    xlabel('\lambda (\mum)','fontsize',20)
    ylabel('Spectral exitance (W/cm^2/\mum)','fontsize',20) %for I2
    title('Blackbody Radiation','fontsize',24)
    ax=gca;
    ax.XRuler.Exponent=0;
    xlim([0 20])
end

[Walter Roberson]

Do you care about the case where some of the y values might be negative?

[Emmanuel Sarpong]

Yes I do care. I am trying to also figure out how to integrate the shaded portion under each curve (after being able to do the shading or patching properly) so I am trying to stay within the region of interest. Thanks

Answer 1

[Star Strider]

I posted this in response to your Comment (I’ve since deleted my responding Comment), so I’m now posting it as an Answer here —

c=3*10^8; % speed of light in vaccum
h=6.626*10.^-34; %  Planck constant 
k=1.38*10.^-23; %   Boltzmann constant
T=[700 900]; % Temperatures in Kelvin
Lam=(0.0:0.01:50).'*1e-6; % in meters
Lv = (Lam <= 5E-6) & (Lam >= 3E-6);                                                                                     % <— ADDED
cm = [0 0 1; 1 0 0];                                                                                                    % <— ADDED
figure(1)
for i=1:2
    A2(:,i)=(2*pi*h*c*c)./((Lam.^5).*(exp((h.*c)./(k.*T(i).*Lam))-1));
    hold on
    plot(Lam*1e6,A2(:,i)*1e-10,'r','linewidth',2) 
    x = Lam*1e6;    % Define x  For patch                                                                                   % <— CHANGED
    y(:,i) = A2(:,i)*1e-10; % Define y For patch                                                                            % <— CHANGED
    if i == 1
        patch([x(Lv); flip(x(Lv))], [zeros(size(y(Lv,1))); flip(y(Lv,i))], cm(i,:), 'FaceAlpha',0.5, 'EdgeColor','none')    % <— CHANGED
    elseif i == 2
        patch([x(Lv); flip(x(Lv))], [y(Lv,1); flip(y(Lv,2))], cm(i,:), 'FaceAlpha',0.5, 'EdgeColor','none')                 % <— CHANGED
    end
    hold off
    xlabel('\lambda (\mum)','fontsize',20)
    ylabel('Spectral exitance (W/cm^2/\mum)','fontsize',20) %for I2
    title('Blackbody Radiation','fontsize',24)
    ax=gca;
    ax.XRuler.Exponent=0;
    xlim([0 20])
end

.

[Emmanuel Sarpong]

It spits out error message on where you define the y patch. Message reads 'unable to perfoem assignment because the size of the left side is 1-by-1 and the size of the right side is 5001-by-1'. Thanks

[Rik]

As you can see, the posted code works. If you have an error, that means you used different code (or used a script and forgot to use clearvars).

You should post the code you used and use the green triangle to run your code.

[Star Strider]

I transposed ‘Lam’ to become a column vector so now all the appropriate vectors are column-oriented. With that necessary change, everything works.

See the ‘Statistics’ matrix at the end of the code (delete it later) —

c=3*10^8; % speed of light in vaccum
h=6.626*10.^-34; %  Planck constant 
k=1.38*10.^-23; %   Boltzmann constant
T=[700 900]; % Temperatures in Kelvin
Lam=(0.0:0.01:50).'*1e-6; % in meters
Lv = (Lam <= 5E-6) & (Lam >= 3E-6);                                                                                     % <— ADDED
cm = [0 0 1; 1 0 0];                                                                                                    % <— ADDED
figure(1)
for i=1:2
    A2(:,i)=(2*pi*h*c*c)./((Lam.^5).*(exp((h.*c)./(k.*T(i).*Lam))-1));
    hold on
    plot(Lam*1e6,A2(:,i)*1e-10,'r','linewidth',2) 
    x = Lam*1e6;    % Define x  For patch                                                                                   % <— CHANGED
    y(:,i) = A2(:,i)*1e-10; % Define y For patch                                                                            % <— CHANGED
    if i == 1
        patch([x(Lv); flip(x(Lv))], [zeros(size(y(Lv,1))); flip(y(Lv,i))], cm(i,:), 'FaceAlpha',0.5, 'EdgeColor','none')    % <— CHANGED
    elseif i == 2
        patch([x(Lv); flip(x(Lv))], [y(Lv,1); flip(y(Lv,2))], cm(i,:), 'FaceAlpha',0.5, 'EdgeColor','none')                 % <— CHANGED
    end
    hold off
    xlabel('\lambda (\mum)','fontsize',20)
    ylabel('Spectral exitance (W/cm^2/\mum)','fontsize',20) %for I2
    title('Blackbody Radiation','fontsize',24)
    ax=gca;
    ax.XRuler.Exponent=0;
    xlim([0 20])
end

Statistics = [size(Lam); size(A2); size(x); size(y)];
fprintf(1,'Statistics:\n\tsize(Lam) = [%4d %4d]\n\tsize(A2)  = [%4d %4d]\n\tsize(x)   = [%4d %4d]\n\tsize(y)   = [%4d %4d]\n', Statistics.')

Statistics:
	size(Lam) = [5001    1]
	size(A2)  = [5001    2]
	size(x)   = [5001    1]
	size(y)   = [5001    2]

.

[Emmanuel Sarpong]

All is perfect now. Adding the clearvars did it. Thanks a lot

[Star Strider]

As always, my pleasure!