How to plot the quadratic function surface?

Question

Seyyed Mohammad Saeed Damadi 2019-2-17

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/445363-how-to-plot-the-quadratic-function-surface

回答： Naman Bhaia 2019-2-27

采纳的回答： Naman Bhaia

在 MATLAB Online 中打开

I want to plot

when

. I wrote the following codes and was wondering if there is a more efficient way with less number of lines:

clc
clear
Q = [0.7750, 0.3897; 0.3897 0.3250];
b = [-2,-1];
[X,Y] = meshgrid(-5:0.1:1);
x = X(:);
y = Y(:);
sx = size(X);
n = length(x);
z = zeros(n,1);
for i = 1:n
 z(i) = 0.5*[x(i,1),y(i,1)]*Q*[x(i,1);y(i,1)] - b*[x(i,1);y(i,1)];
end
X = reshape(x,sx);
Y = reshape(y,sx);
Z = reshape(z,sx);
surf(X,Y,Z)

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Answer 1

Naman Bhaia 2019-2-27

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/445363-how-to-plot-the-quadratic-function-surface#answer_362976

在 MATLAB Online 中打开

Hey Seyyed,

I was able to simplify the code by using vectorized operations instead of for loop

clc
clear
Q = [0.7750 0.3897; 0.3897 0.3250];
b = [-2 -1];
[X,Y] = meshgrid(-5:0.1:1);
x = X(:);
y = Y(:);
sx = size(X);
a=0.5*diag([x y]*Q*[x';y'])-(b*[x';y'])';
Z = reshape(a,sx);
surf(X,Y,Z)