要将曲线拟合到一组点上,我们可以使用ordinary least-squares回归。 MathWorks有一个描述过程的solution page。
举个例子,让我们用一些随机数据开始:
% some 3d points
data = mvnrnd([0 0 0], [1 -0.5 0.8; -0.5 1.1 0; 0.8 0 1], 50);
由于@BasSwinckels表明,通过构建所需的design matrix,您可以使用mldivide
或pinv
到solve the overdetermined system表示Ax=b
:
% best-fit plane
C = [data(:,1) data(:,2) ones(size(data,1),1)] \ data(:,3); % coefficients
% evaluate it on a regular grid covering the domain of the data
[xx,yy] = meshgrid(-3:.5:3, -3:.5:3);
zz = C(1)*xx + C(2)*yy + C(3);
% or expressed using matrix/vector product
%zz = reshape([xx(:) yy(:) ones(numel(xx),1)] * C, size(xx));
接下来我们可以看到结果:
% plot points and surface
figure('Renderer','opengl')
line(data(:,1), data(:,2), data(:,3), 'LineStyle','none', ...
'Marker','.', 'MarkerSize',25, 'Color','r')
surface(xx, yy, zz, ...
'FaceColor','interp', 'EdgeColor','b', 'FaceAlpha',0.2)
grid on; axis tight equal;
view(9,9);
xlabel x; ylabel y; zlabel z;
colormap(cool(64))
正如提到的,我们可以通过添加更多方面的独立变量矩阵(在A
在Ax=b
)得到高阶多项式拟合。假设我们想要拟合具有常数,线性,相互作用和平方项(1,x,y,xy,x^2,y^2)的二次模型。我们可以手动执行此操作:
% best-fit quadratic curve
C = [ones(50,1) data(:,1:2) prod(data(:,1:2),2) data(:,1:2).^2] \ data(:,3);
zz = [ones(numel(xx),1) xx(:) yy(:) xx(:).*yy(:) xx(:).^2 yy(:).^2] * C;
zz = reshape(zz, size(xx));
还有一个辅助函数x2fx
在统计工具箱,有助于构建设计矩阵的一对夫妇模型订单:
C = x2fx(data(:,1:2), 'quadratic') \ data(:,3);
zz = x2fx([xx(:) yy(:)], 'quadratic') * C;
zz = reshape(zz, size(xx));
最后有一个很好的功能polyfitn
由John D'Errico在文件交换中允许您指定所涉及的各种多项式次序和项:
model = polyfitn(data(:,1:2), data(:,3), 2);
zz = polyvaln(model, [xx(:) yy(:)]);
zz = reshape(zz, size(xx));
如何在python中执行同样的操作..!?位帮助将升值... @Amro – diffracteD
@diffracteD:我将代码翻译成Python:https://gist.github.com/amroamroamro/1db8d69b4b65e8bc66a6 – Amro
感谢您的帮助...我一定会尝试它.. ! – diffracteD