How to plot this equation to obtain the figure?

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soe min aung 2019-12-18

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https://ww2.mathworks.cn/matlabcentral/answers/497178-how-to-plot-this-equation-to-obtain-the-figure

评论： soe min aung 2019-12-24

采纳的回答： Walter Roberson

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Walter Roberson 2019-12-18

You have a bit of a problem: your has three independent inputs, and one output, so you need a 4-dimensional plot . The plot c that you show is for a fixed time, t1, not the general equation.

If you have the Symbolic Toolbox, probably the easiest approach is to use a piecewise() equation, subs() in a fixed time, and fplot() the result. If you do not have the Symbolic Toolbox, either use logical indexing to construct your answer, or else just compute over the three y ranges separately and concatenate them together.

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Answer 1

Walter Roberson 2019-12-24

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https://ww2.mathworks.cn/matlabcentral/answers/497178-how-to-plot-this-equation-to-obtain-the-figure#answer_407549

在 MATLAB Online 中打开

N = 50;   %subdivisions per dimension
xmin = -1; xmax = 101;
ymin = -160; ymax = 160;
tmin = 0; tmax = 3600;
xvec = linspace(xmin, xmax, N);
yvec = linspace(ymin, ymax, N);
tvec = linspace(tmin, tmax, N);
[X, Y, T] = ndgrid(xvec, yvec, tvec);
maskx = 0 <= X & X <= 100;
masky1 = -150 <= Y & Y < -50;
masky2 = -50 <= Y & Y < 50;
masky3 = 50 <= Y & Y <= 150;
xi = zeros(size(X));
mask1 = maskx & masky1;
mask2 = maskx & masky2;
xi(mask1) = xi0 * v*T(mask1)/(2 * L) .* (1 - cos(pi/50*X(mask1))) .* (1 - cos(pi/100*(Y(mask1) + 150)));
xi(mask2) = xi0 * V*T(mask2) / L .* (1-cos(pi/50*X(mask2)));
xi(mask3) = xi0 * v*T(mask3)/(2 * L) .* (1 - cos(pi/50*X(mask3))) .* (1 - cos(pi/100*(Y(mask3) - 150)));
random_time_idx = randi(length(tvec));
random_time = tvec(random_time_idx);
x_for_t = X(:,:,random_time_idx);
y_for_t = Y(:,:,random_time_idx);
zi_for_t = xi(:,:,random_time_idx) / xi0;
surf(x_for_t, y_for_t, zi_for_t)
xlabel('x (km)');
ylabel('y (km)');
zlabel('$\frac{\zi(x,y,t1)}{\zi_0}', 'interpreter', 'latex')
title( sprintf('time = %.2f', random_time) );

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soe min aung 2019-12-24

在 MATLAB Online 中打开

Thank you for your response. I have Symbolic Toolbox. Let me show you a plot form allwayzitzme@gmail.com which is the same your figure from your code. But It is different from the above picture. I want to get as above figure. But I can't try this. So I need your advice for this code. Please try sir,

clc
clear all
m = 30 ; n = 10 ; 
x = linspace(0,100,m) ; 
eta0 = 2 ; 
L = 100 ; 
W = 100 ; 
v = 0.14 ; 
t = 5.95 ; 
y1 = linspace(-150,-50,n) ; 
[X,Y1] = meshgrid(x,y1) ; 
T1 = eta0*v*t/(2*L)*(1-cos(pi/50*X)).*(1-cos(pi/100*(Y1+150))) ; 
y2 = linspace(-50,50,n) ; 
[X,Y2] = meshgrid(x,y2) ; 
T2 = eta0*v*t/L*(1-cos(pi/50*X)) ; 
y3 = linspace(50,150,n) ; 
[X,Y3] = meshgrid(x,y3) ; 
T3 = eta0*v*t/(2*L)*(1-cos(pi/50*X)).*(1-cos(pi/100*(Y3-150))) ; 
X = [X ; X; X] ; 
Y = [Y1 ; Y2 ;Y3] ; 
eta = [T1 ; T2 ; T3] ; 
surf(X,Y,eta) ;