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It is difficult to control the range

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재훈
재훈 on 16 May 2024
Commented: 재훈 on 21 May 2024 at 8:29
Hellow there. I want to connect functions with different scopes, but it doesn't work. Where did I go wrong? Have a nice day everyone
here is my code
clc; clear all; close all;
A = readmatrix('w10_data.xlsx','Sheet','Sheet1');
x = A(:,1);
fx = A(:,2);
%1D linear interpolation
xspace = [];
px = [];
for i = 1:3
x_segment = linspace(x(i), x(i+1),101);
p_segment = fx(i) + (fx(i+1) - fx(i))/(x(i+1)-x(i))*(x_segment-x(i));
xspace = [xspace x_segment(1:end-1)];
px = [px p_segment(1:end-1)];
end
% Polynomial interpolation
xspace2 = 4:0.01:7;
Lx = zeros(1,length(xspace2));
for j = 1:size(x,1)
lj = 1;
for m = 1:size(x,1)
if m == j
continue
end
lj = lj .*(xspace2 -x(m))/((x(j)-x(m)));
end
Lx = Lx + fx(j)*lj;
end
% Cubic spline interpolation
xspace3 = 7:0.01:10;
S = spline(x(7:end),fx(7:end),xspace3);
%S = spline(x,fx,xspace2);
figure(1)
scatter(x,fx,'k','filled'); hold on;
plot(xspace,px,'b'); hold on;
plot(xspace2,Lx,'r'); hold on;
plot(xspace2,S,'g'); hold on;
xlim([0 12]);
ylim([0 20]);

Accepted Answer

Pratyush Swain
Pratyush Swain on 16 May 2024
Hi 재훈,
From the code snippet you have provided , I can make out an observation as follows:
  • Plotting Issue with Cubic Spline: The line "plot(xspace2,S,'g')" seems to be incorrect because "xspace2" is used for polynomial interpolation, not for cubic spline interpolation. You probably meant to plot "xspace3" against "S" for the cubic spline part:
plot(xspace2,Lx,'r'); hold on;
% Correcting the following line
% plot(xspace2,S,'g'); hold on;
plot(xspace3,S,'g'); hold on;
% -----------------------------
After making the above change, I am getting the plot figure as follows:
For more information please refer to: https://www.mathworks.com/help/matlab/ref/spline.html
Hope this is what you were looking for.
  2 Comments
재훈
재훈 on 16 May 2024
Oh my mistake. Thank you for your help. Have a nice day! :)
Image Analyst
Image Analyst on 16 May 2024
If this Answer solves your original question, then could you please click the "Accept this answer" link to award the answerer with "reputation points" for their efforts in helping you? They'd appreciate it. Thanks in advance. 🙂 Note: you can only accept one answer (so pick the best one) but you can click the "Vote" icon for as many Answers as you want. Voting for an answer will also award reputation points.

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More Answers (1)

Image Analyst
Image Analyst on 16 May 2024
See my attached splines demos.
  1 Comment
재훈
재훈 on 21 May 2024 at 8:29
Sorry for checking late. Nonetheless, it helped me a lot. Thank you for your help. have a good day!

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