I'm getting a wrong table result from my function.

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Seungryul Lee 2022-5-1

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1709480-i-m-getting-a-wrong-table-result-from-my-function

评论： Torsten 2022-5-2

I made a table of results that includes h and the error: Eh = max|y(t) − y ̃(t)|, where y ̃ is my approximated solution. I'm using twostepmethod function with startingtimet =0, endingtimet =20, and stepsizes: h= 1/2^n for n=1, . . . , 10.

And I'm getting a totally wrong table which is

 Table with h & Eh
    h          Eh
0e+225 *
0000    0.0000
0000    0.0000
0000    0.0000
0000    4.2965
0000       Inf
0000       Inf
0000       Inf
0000       Inf
0000       Inf
0000       Inf

Can you please fix my code to get a proper table?

this is my code

f=@(t,y) -y-3*t;
F=@(t) 3-3*t-2*exp(-t);
t0=0; y0=1;
te=20;
nn=1:10;
h = 1./2.^nn;
for ii=1:length(nn)
    [ys, ts] = MyTwoStepMethod(f, t0, te, y0, h(ii));
    Eh(ii) = max(abs(F(ts)-ys));
end
disp('Table with h & Eh'), disp('    h          Eh')
disp([h',Eh'])

and this is my function

function [ys, ts] = MyTwoStepMethod(f, t0, te, y0, h)
ts = t0:h:te;
ys(1,1) = y0;
ys(1) = y0;
ys(2) = y0 + h*f(ts(1),ys(1));
for i = 2:length(ts)-1
    ys(i+1) = -4*ys(i) + 5*ys(i-1) + h*(4*f(ts(i),ys(i))+2*f(ts(i-1),ys(i-1)));
end
end		