How can I use various colors to fill the area under a normal distribution curve?

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Navid on 28 Nov 2023
Commented: Star Strider on 28 Nov 2023
Hi, I obtained a probability distribution for my data using the following syntax:
h = histfit(data);
and then:
pd = fitdist(data,'Normal');
I want to create a graph similar to Figure 1 using the mean and standard deviation values obtained from the histogram and fitted distribution.
In advance, I would like to express my gratitude for your assistance.
Figure 1:
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Accepted Answer

Star Strider on 28 Nov 2023
Sure!
Try this —
x = linspace(1.5, 5, 250);
mu = 3.3;
s = 0.6;
y = normpdf(x, mu, s);
figure
plot(x, y)
hold on
Lv1 = (x>=mu) & (x<mu+s);
patch([x(Lv1) flip(x(Lv1))], [zeros(size(y(Lv1))) flip(y(Lv1))], 'g', 'EdgeColor','none')
Lv2 = (x>=mu+s) & (x<mu+2*s);
patch([x(Lv2) flip(x(Lv2))], [zeros(size(y(Lv2))) flip(y(Lv2))], 'y', 'EdgeColor','none')
Lv3 = (x>=mu+2*s) & (x<mu+3*s);
patch([x(Lv3) flip(x(Lv3))], [zeros(size(y(Lv3))) flip(y(Lv3))], 'r', 'EdgeColor','none')
hold off
If you want the text annotations as well, I can supply those, and the vertical lines, too.
.
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Navid on 28 Nov 2023
Thank you for your assistance. The second option was correctly implemented in my version. Thank you again.
Star Strider on 28 Nov 2023
As always, my pleasure!

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More Answers (2)

Angelo Yeo on 28 Nov 2023
f = @(x, mu, sd) 1/(sd*sqrt(2*pi)) * exp(-1/2*((x-mu)/sd).^2);
x = linspace(1.5, 5, 1000);
mu = 3.25; sd = 0.5;
figure;
hold on;
x_zone1 = linspace(mu, mu+sd, 300);
x_zone2 = linspace(mu+sd, mu+2*sd, 300);
x_zone3 = linspace(mu+2*sd, mu+3*sd, 300);
area(x_zone1, f(x_zone1, mu, sd), 'FaceColor', 'g')
area(x_zone2, f(x_zone2, mu, sd), 'FaceColor', 'y')
area(x_zone3, f(x_zone3, mu, sd), 'FaceColor', 'r')
plot(x, f(x, mu, sd), 'color','k', 'linewidth', 2);
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Chunru on 28 Nov 2023
Edited: Chunru on 28 Nov 2023
data = randn(8192, 1);
h = histfit(data);
pd = fitdist(data,'Normal')
pd =
NormalDistribution Normal distribution mu = -0.00241653 [-0.0240676, 0.0192345] sigma = 0.999681 [0.984606, 1.01523]
figure;
x = linspace(-4*pd.sigma, 4*pd.sigma, 1001);
p = pdf(pd, x);
figure;
plot(x, p);
hold on
facecolor =["g", "y", "r"]
facecolor = 1×3 string array
"g" "y" "r"
for i=1:3
idx = (x >= (i-1)*pd.sigma) & (x < i*pd.sigma);
area(x(idx), p(idx), FaceColor=facecolor(i))
end
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Chunru on 28 Nov 2023
It seems that you are using older version of matlab. Use the following name-value syntax for older version matlab.
area(x(idx), p(idx), 'FaceColor', facecolor(i))
Navid on 28 Nov 2023
Dear Chunru
I wanted to express my gratitude for the assistance you provided. I successfully modified your code and achieved my desired outcome thanks to your guidance. I appreciate your help.
mu = pd.mu; sd = pd.sigma;
x = linspace(mu-4*pd.sigma,mu+4*pd.sigma,1001);
p = pdf(pd,x);
figure;
plot(x,p);
hold on
facecolor=['g','y','r'];
for i=1:3
idx = (x>= mu+(i-1)*pd.sigma)&(x<mu+i*pd.sigma);
area(x(idx), p(idx), 'FaceColor', facecolor(i))
end

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