gap in the plot

How can I make the red plot start in the same place (from 1)?

Answer 1

[Walter Roberson]

red_x = red_x - min(red_x) + 1;
plot(blue_x, blue_y, 'b', red_x, red_y, 'r')

[Valeria Pinus]

This has just created a gap on the other side and moved the whole plot :(

[Walter Roberson]

Yes, that is to be expected. You did not specify that was not to happen.

It looks to me as if whatever process generated the data for the red line did not start from the same position. However, you have not given us any information about how the red line was generated, so we can only make wild guesses.

[Valeria Pinus]

My bad. Here is the code:

X=[1 2 3 4 5 6 7 8 9]; %госдолг сша
Y=[120.7 26.0 162.0 50.7 256.9 290.5 380.9 90.9 20.6];
xzv=5.5;
xi=min(X):0.05:max(X);            % Вспомогательный вектор абсциссы
yi=spline(X,Y,xi);
plot(X,Y,'*k',xi,yi,'b');grid;hold on;           % Построение графика
AS=[2 1 0 0 0 0 0 0 0;
    1 4 1 0 0 0 0 0 0;
    0 1 4 1 0 0 0 0 0;
    0 0 1 4 1 0 0 0 0;
    0 0 0 1 4 1 0 0 0;
    0 0 0 0 1 4 1 0 0;
    0 0 0 0 0 1 4 1 0;
    0 0 0 0 0 0 1 4 1;
    0 0 0 0 0 0 0 1 2];
BS=3.*[26.0-120.7;162.0-120.7;50.7-26.0;
       256.9-162.0;290.5-50.7;380.9-256.9;
       90.9-290.5;20.6-380.9;20.6-90.9];
S=AS\BS
s3x=form2(X,Y,S,xzv)                 %значение s3(x*)
dx=(max(X)-min(X))/50;             % Вычисление шага
     for i=(1:50)
        xi_new(i)=min(X)+dx*i;              % Вспомогательные точки абсциссы
        zi(i)=form2(X,Y,S,xi_new(i));          % Значение S3 в точке xi(i)
        
     end
plot(X,Y,'*k',xi_new,zi,'r');hold off;        % Построение графика

form2:

 function y=form2(X,Y,S,z);
       i=max(find(X<z));
       h=X(i+1)-X(i);
       p=(X(i+1)-z)/h;
       q=(z-X(i))/h;

   y=p^2*(2*q+1)*Y(i)+p^2*q*S(i)+...
     q^2*(2*p+1)*Y(i+1)-q^2*p*S(i+1);

[Walter Roberson]

Perhaps

xi_new(i)=min(X)+dx*i;

should be

xi_new(i)=min(X)+dx*(i-1);

?

[Valeria Pinus]

that way it says

Unable to perform assignment because the left and right sides have a different number of elements.

Error in lesson5_1 (line 24)

zi(i)=form2(X,Y,S,xi_new(i));

[Walter Roberson]

I see.

Your processing requires a gap. In form2 you have

       i=max(find(X<z));

which would be empty if z is exatly equal to the first X because you are attempting to process right to the left margin.

You can reduce the width of the gap by reducing dx, but you cannot eliminate the gap.