false position method to find zeros, not plotting zeros

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Rachel Dawn 2018-2-26

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/384779-false-position-method-to-find-zeros-not-plotting-zeros

编辑： Rachel Dawn 2018-2-26

Can someone tell me why this code is not finding/ plotting the roots for my function? I created a plot for function. Then, I wrote the code for false position method to solve for all the zeros of that function (using three x ranges, where I know the three roots are within). Then, I tried to overlay the plot of these zeros onto my old plot.

this is my function file:

function result = lalafunction(x)
  result= (2*x.*exp(cos(3*x)).*exp(-x)) + 70 ;

this is my plot file:

plot=figure(2),
x1= -3.5:0.01:-1.5;
for i=1:length(x1)
g(i)=lalafunction(x1(i));
end 
plot(x1,g)

this is the file that should plot the zeros. It finds the first two, but not the last one correctly

    plot(x1,g)
       hold on
      xo= [-1.99,-1.90; -2.8,-2.5; -3.3,-3.2];
      for ii=1:3
      xleft=xo(ii,1);
      xright=xo(ii,2);
      iteration=1;
      while iteration<=100 && abs(xleft-xright)> 10^-3 
      yleft=lalafunction(xleft);
      yright=lalafunction(xright);
      xm = xright-((yright*(xright-xleft))/(yright-yleft));
      if yleft*lalafunction(xm) < 0
      xright=xm;
      else 
      xleft=xm;
      end 
      iteration = iteration +1;
      end 
      xx(ii)= (xleft+xright)/2
      yy(ii)= lalafunction(xx(ii))
      end
      plot (xx,yy,'o')