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I'm trying to demonstrate a concept like Fourier Transform. While searching the web, I encountered an image in Wikipedia:

Is that possible to plot this figure in Python or MATLAB?

Have a look at the documentatin of plot3 and patch as well as some standard plot tools.

This code produces the following image:

t = 0:.01:2*pi;

x1 = 1/2*sin(2*t);

x2 = 1/3*sin(4*t);

x3 = 1/4*sin(8*t);

x4 = 1/6*sin(16*t);

x5 = 1/8*sin(24*t);

x6 = 1/10*sin(30*t);



step = double(x1>0);

step(step==0) = -1;

step = step*.5;



figure

hold on

plot3(t,ones(size(t))*0,step,'r')



plot3(t,ones(size(t))*1,x1,'b')

plot3(t,ones(size(t))*2,x2,'b')

plot3(t,ones(size(t))*3,x3,'b')

plot3(t,ones(size(t))*4,x4,'b')

plot3(t,ones(size(t))*5,x5,'b')

plot3(t,ones(size(t))*6,x6,'b')



plot3([2*pi+.5 2*pi+.5],[.5 6],[0 0],'b')

plot3([2*pi+.5 2*pi+.5],[1 1],[0 1/2],'b')

plot3([2*pi+.5 2*pi+.5],[2 2],[0 1/3],'b')

plot3([2*pi+.5 2*pi+.5],[3 3],[0 1/4],'b')

plot3([2*pi+.5 2*pi+.5],[4 4],[0 1/6],'b')

plot3([2*pi+.5 2*pi+.5],[5 5],[0 1/8],'b')

plot3([2*pi+.5 2*pi+.5],[6 6],[0 1/10],'b')



hold off

view([45,45])

patch([0 2*pi 2*pi 0 0],[0 0 0 0 0],[-1 -1 1 1 -1],'g','FaceAlpha',.3,'EdgeColor','none')

patch([2*pi+.5 2*pi+.5 2*pi+.5 2*pi+.5 2*pi+.5],[.5 6 6 .5 .5],[-1 -1 1 1 -1],'g','FaceAlpha',.3,'EdgeColor','none')



zlim([-1,1])

xlim([-.5,2*pi+.5])

ylim([-.5,6.5])



axis off

It could serve you as a start point.

Since you already read the article about fft I leave the red plot as an exercise to yourself ;-)

The function to plot 3D lines is plot3

The following code will produce the various lines

T=(0:.01:2).';

X = repmat(1:6,[length(T),1]);

phase = bsxfun(@times,T*2*pi,1:2:11);

Z = 4/pi*bsxfun(@rdivide,sin(phase),1:2:11);



Xsum = zeros(size(T));

Zsum = sum(Z,2);



figure;

plot3(X,T,Z,'b');

hold on

plot3(Xsum,T,Zsum,'r');

patch objects with an alpha channel can be used for the grey surfaces.

Xpatch=zeros(4,1);

Ypatch= [0 2 2 0].';

Zpatch= [2 2 -2 -2].';

patch(Xpatch,Ypatch,Zpatch,[.5 .5 .5],'FaceAlpha',.3,'EdgeColor',[.5 .5 .5]);

% patch(X,Y,Z,FaceColor_RGB_triplet,'Name','Value',...)

% FaceAlpha : transparency

% EdgeColor : RGB triplet for the edge

The same can be used to plot the frequency spectrum