i need help with this question

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dulanga 2019-5-7

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https://ww2.mathworks.cn/matlabcentral/answers/460683-i-need-help-with-this-question

评论： dulanga 2019-5-7

I am supposed to find the number of timesteps i.e the number of steps taken but my answer is incorrect any inputs on my code will be a major help thanks.Also has the advection equation with the center spaced method used correctly ?

N=200;
x=linspace(-10,10,N);
dx=x(2)-x(1);
c=-0.9;
t=0;
dt=0.2;
timestep=0;
f=@(x)exp(-5*x.^2);
y=f(x)';
figure(1),plot(x,y)
title(['Current time=',num2str(t)])
drawnow
%using centered space 
A=eye(N)-(0.5*c*(dt/dx))*((diag(ones(N-1,1),1)-diag(ones(N,1),0)));
while abs(y(end))<0.001 && abs(y(1))<0.001
    y=A*y;
    t=t+dt;
    timestep=timestep+1;
    figure(1),cla
    plot(x,y)
    hold on
    plot(x,f(x-c*t),'r')
    title(['Current time=',num2str(t)])
    drawnow
end

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Torsten 2019-5-7

编辑：Torsten 2019-5-7

You forgot the parenthesis around the difference of the diag-expressions.

And it must be dt/dx instead of dx/dt.

dulanga 2019-5-7

在 MATLAB Online 中打开

thanks alot how would u implemnt this

N=1000;
x=linspace(-10,10,N);
dx=x(2)-x(1);
c=2.6;
t=0;
dt=0.2;
timestep=0;
f=@(x)exp(-5*x.^2);
y=f(x)';
figure(1),plot(x,y)
title(['Current time=',num2str(t)])
drawnow
%using lax 
A=eye(N)-(0.5*c*(dt/dx))*diag(ones(N-1,1),1)-diag(ones(N-1,1),-1);
while abs(y(end))<0.001 && abs(y(1))<0.001
    y=A*y;
    t=t+dt;
    timestep=timestep+1;
    figure(1),cla
    plot(x,y)
    hold on
    plot(x,f(x-c*t),'r')
    title(['Current time=',num2str(t)])
    drawnow
end