Quadratic Spline Interpolation Code

Question

Kimberlin Sookchand 2020-4-28

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https://ww2.mathworks.cn/matlabcentral/answers/521245-quadratic-spline-interpolation-code

编辑： John D'Errico 2020-12-14

What is the MATLAB code for quadratic splines? As linear uses interp1 linear and cubic splines uses interp1 spline. What is the corresponding interp1 coding for quadratic splines?

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darova 2020-4-28

Matlab has no quadratic spline

Try FILEEXCHANGE

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Answer 1

Ameer Hamza 2020-4-28

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https://ww2.mathworks.cn/matlabcentral/answers/521245-quadratic-spline-interpolation-code#answer_428883

编辑：Ameer Hamza 2020-4-28

在 MATLAB Online 中打开

You can write your own quadratic spline function

function yq = quadSpline(x, y, xq)    
    X = [x(:).^2 x(:) ones(size(x(:)))];
    coff = X\y(:);
    yq = [xq(:).^2 xq(:) ones(size(xq(:)))]*coff;
end

Example

x = 1:10;
y = x.^2 + 5 + rand(size(x))*10;
xq = linspace(0,10);
yq = quadSpline(x, y, xq);
plot(x, y, 'r+', 'MarkerSize', 10, 'LineWidth', 2);
hold on
plot(xq, yq, 'b-');

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Enes Senel 2020-12-14

splines should pass from data points. This seems like polynomial regression

John D'Errico 2020-12-14

编辑：John D'Errico 2020-12-14

The comments are correct. This is NOT a quadratic spline tool. All that is given in this answer is a quadratic polynomial regression. That is not a spline. The comment about a spline passing through the data points is not always correct though. An INTERPOLATING spline passes through the data points. However, regression or smoothing splines need not do so. But as said, this still is not a spline, in the sense that a spline is a piecewise function.

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