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

Question

Emmanuel Sarpong 2023-8-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2012642-how-to-color-or-patch-the-region-between-a-curve-and-the-x-axis

评论： Star Strider 2023-8-25

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

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Walter Roberson 2023-8-25

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

Emmanuel Sarpong 2023-8-25

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

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Answer 1

Star Strider 2023-8-25

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2012642-how-to-color-or-patch-the-region-between-a-curve-and-the-x-axis#answer_1293837

在 MATLAB Online 中打开

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

.

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Star Strider 2023-8-25

在 MATLAB Online 中打开

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 2023-8-25

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

Star Strider 2023-8-25

As always, my pleasure!

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