Spline fitting with repeated X's

so here is my matlab code, and the problem is there is repeated x values and spline fit code doesn't work how can i make it so it only takes the first x and doesn't take the repeated ones? And im not good at matlab so, can you please show how to add the code or add it to the original code.

    load Pvst1.txt
    load Fvst1.txt
    tx = Pvst1(:,1);
    tF = Fvst1(:,1);
    x = Pvst1(:,2);
    F = Fvst1(:,2);
    tq=0:0.01:5.81;
    Fq = interp1(tF,F,tq,'spline');
    xq = interp1(tx,x,tq,'spline');
    plot(xq,Fq,'ko');
    hold on
    xlabel('Position (m)','Fontsize',24)
    ylabel('Force (N)','Fontsize',24)
    title('Force vs. Position for car, Part A','Fontsize',24)
    grid on
    hold on

Answer 1

[Torsten]

tx and tF must be monotonically increasing without repeating values, but this is the case for your data. The x and F arrays do not matter. So everything should be o.k. for spline interpolation.

Do you get an error message ?

Replacing

tq=0:0.01:5.81;

by

tq=max(tx(1),tF(1)):0.01:min(tx(end),tF(end));

might help.

Best wishes

Torsten.

[Olca Orakci]

when i press run i doesn't give any error but there is no spline fit in the graph, when i try to add it from tools it gives an error saying there is multiple x values.

[Torsten]

The spline fit is done when you calculate xq and Fq.

You shouldn't request a spline for the plotting of Fq vs. xq.

Best wishes

Torsten.

[Olca Orakci]

i know, but shouldn't spline fit connect the dots?

[Torsten]

If you choose

plot(xq,Fq,'-ok')

the points are automatically connected by a solid line :-)

Best wishes

Torsten.

[Olca Orakci]

Nice, thanks for the help, and have a good day sir.

[dror yemini]

also look at this https://www.mathworks.com/matlabcentral/answers/472849-spline-interpolation-image-way-to-connect