It is difficult to control the range

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]);

Answer 1

[Pratyush Swain]

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.

[재훈]

Oh my mistake. Thank you for your help. Have a nice day! :)

[Image Analyst]

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Answer 2

[Image Analyst]

See my attached splines demos.

[재훈]

Sorry for checking late. Nonetheless, it helped me a lot. Thank you for your help. have a good day!