Problem with plot in interval

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valerio auricchio 2019-4-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/454001-problem-with-plot-in-interval

评论： Walter Roberson 2019-4-3

在 MATLAB Online 中打开

I have a problem with this code:

When i give in input this:

fzer0(@(x)x.^2-4,[0 4])

Matlab give me a good plot.

When i give in input this:

fzer0(@(x)x.^2-4,[0 13])

Matlab give me a wrong plot, the output have not a plot!!

plot(fun(xo(1):0.00001:xo(2)), 'b - ', 'LineWidth', 2.5);
grid on;
yline(0, '--r', 'y = 0');
xlabel('x');
str=func2str(fun); %stringa della funzione
newstr=erase(str(5:end), '.'); %cancella dall'espressione il function handle e cancella il punto
tit=strcat('f = ', newstr); 
title(tit);
text(double(m), double(0), strcat( 'x = ', num2str(m) ) );
set(gcf, 'color', 'g');
set(gca, 'FontSize', 9);

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valerio auricchio 2019-4-2

在 MATLAB Online 中打开

Fun is a function that in the 2 case is x^2-4.

this is the code for xo(1) and xo(2):

while(abs(diff(xo))>= p.Results.TOL*max(abs(xo)) && abs(fun(m))>TOLF && nit<p.Results.NMAX)
    if(fun(m)*fun(xo(1))<0)
        xo(2)= m;
    else
        xo(1)= m;
    end
    nit=nit+1;
    m = xo(1)+0.5*diff(xo);
end
if(abs(diff(xo))> p.Results.TOL*max(abs(xo)) && abs(fun(m))>TOLF && nit==p.Results.NMAX)
    warning("limit reached... calculation stop! ");
end
x=m;
output.fx = fun(x);
output.niter = nit;