gap in the plot

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Valeria Pinus 2019-10-31

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/488482-gap-in-the-plot

评论： Walter Roberson 2019-10-31

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

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Answer 1

Walter Roberson 2019-10-31

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https://ww2.mathworks.cn/matlabcentral/answers/488482-gap-in-the-plot#answer_399098

在 MATLAB Online 中打开

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

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Valeria Pinus 2019-10-31

在 MATLAB Online 中打开

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);

Valeria Pinus 2019-10-31

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 2019-10-31

在 MATLAB Online 中打开

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.

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gap in the plot

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gap in the plot

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