用 Matlab 函数实现 Collatz 猜想！拜托了！！在线等！！

function threenplus1(n)

%"Three n plus 1".

% Study the 3n+1 sequence.

% threenplus1(n) plots the sequence starting with n.

% threenplus1 with no arguments starts with n = 1.

% uicontrols decrement or increment the starting n.

% Is it possible for this to run forever?

if ~isequal(get(gcf,'tag'),'3n+1')

shg

clf reset

uicontrol( ...

'position',[260 5 25 22], ...

'string','<', ...

'callback','threenplus1(''<'')')

uicontrol( ...

'position',[300 5 25 22], ...

'string','>', ...

'callback','threenplus1(''>'')')

uicontrol( ...

'position',[480 5 40 22], ...

'string','close', ...

'callback','close(gcf)')

set(gcf,'tag','3n+1')

end

if nargin == 0

n = 1

elseif isequal(n,'<')

n = get(gcf,'userdata') - 1

elseif isequal(n,'>')

n = get(gcf,'userdata') + 1

end

if n <1, n = 1end

set(gcf,'userdata',n)

y = n

while n >1

if rem(n,2)==0

n = n/2

else

n = 3*n+1

end

y = [y n]

end

semilogy(y,'.-')

axis tight

ymax = max(y)

ytick = [2.^(0:ceil(log2(ymax))-1) ymax]

if length(ytick) >8, ytick(end-1) = []end

set(gca,'ytick',ytick)

title(['n = ' num2str(y(1))])

n=27a=1

while n~=1,

    if mod(n,2)==1,

        n = n*3 + 1

    else

        n = n / 2

    end

    if n>a,

        a=n

    end

end

a

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