Problem with the plot of function besselj.

Question

Ricardo Boza Villar 2016-5-18

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/284876-problem-with-the-plot-of-function-besselj

回答： Ricardo Boza Villar 2016-5-19

采纳的回答： Roger Stafford

a76.m

在 MATLAB Online 中打开

I have this code:

nu=1;
whitebg('k')
x=0:1e-3:9;
for n=1:4 
    paso=1/2^(n-1);
    y1=besselj(nu,x); 
    figure(n),close(n),figure(n) 
    hold on 
    plot(x,y1,'b')
    h=1e-5; 
    yder1=(besselj(nu,2+h)-besselj(nu,2))/h;
    yder2=(besselj(nu,8+h)-besselj(nu,8))/h; 
    nodos=2:paso:8; 
    yvalues=besselj(nu,nodos); 
    y2=spline(nodos,[0.009,yvalues,0.5588],x);
    plot(x,y2,'r')
    y3=spline(nodos,[yder1,yvalues,yder2],x);
    plot(x,y3,'w')
    y4=spline(nodos,yvalues,x);
    plot(x,y4,'g') 
    y5=interp1(nodos,yvalues,x); 
    plot(x,y5,'c')
      grid 
      title('Bessel function for nu=1')
      xlabel('Eje x') 
      ylabel('Eje y')
      legend('Besselj','Spline sujeto mal','Spline sujeto bien',...
          'Spline not-a-knot','Interp1','location','best')
  end

But I don't know why the graphs of the function 'besselj' seem to decrease with every iteration. I would like the function 'besselj' to always display the same plot, that's why the variable 'nu' is constant in my script.

Here's the link to function 'besselj':

http://www.mathworks.com/help/matlab/ref/besselj.html

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Answer 1

Roger Stafford 2016-5-18

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/284876-problem-with-the-plot-of-function-besselj#answer_222658

As can be seen on the left side of your graphs, the scaling in the vertical “Eje y” axis is changing. The bessel curves are not really changing. It is the red spline that is getting worse each time. You should use a constant scaling factor in your plotting to see what is actually happening.