Recursion revisited - can you help me?

function v = reversal(v)
if length(v) > 1
    v = [v(end) reversal(v(1:end-1))];
end
end

[Gerry Dumlao]

function v = reversal2(v)
if length(v) > 1
    ii=round(length(v) /2 );
    v = [double(v(ii+1:end)) , double(v(1:ii))];
end
end

[Walter Roberson]

Your second function is not recursive. Also it converts to double for no apparent reason.

[Gerry Dumlao]

i will change it or no?

[Gerry Dumlao]

function v = reversal2(v)
if length(v) > 1
    ii=round(length(v) /2 );
    v = [reversal2(v(ii+1:end)) , reversal2(v(1:ii))];
end
end

is this correct?

[Walter Roberson]

Tests out okay

V = char(randi([33 126], 1, 31))

V = '*^jMW@uXA#]RGVBM3|7;F?6YoAy"_;['

RV = reversal2(V)

RV = '[;_"yAoY6?F;7|3MBVGR]#AXu@WMj^*'

isequal(RV, fliplr(V))

ans = logical
   1

V = char(randi([33 126], 1, 32))

V = 'Q|#`bcXGa;U3(WMtLD2'e;+}mQltHR5g'

RV = reversal2(V)

RV = 'g5RHtlQm}+;e'2DLtMW(3U;aGXcb`#|Q'

isequal(RV, fliplr(V))

ans = logical
   1

function v = reversal2(v)
if length(v) > 1
    ii=round(length(v) /2 );
    v = [reversal2(v(ii+1:end)) , reversal2(v(1:ii))];
end
end

Answer 1

[ghazal]

I have problem and this is my code, anyone can help me?

function v=reversal(v)
if length(v)==1
    ii=round(length(v)/2);
    v=[reversal(v(ii+1:end)) , reversal(v(1:ii))];
end
end

[Walter Roberson]

What should happen if length(v) is not 1? Currently the code returns v unchanged in that case.

If length(v)==1 is true, then you execute the body of the if, and take length(v) which we know must be 1 (otherwise the condition would have been false.) round(1/2) is 1, so ii will always be 1 in that case (no point in computing it.) So you would call reversal(vv(2:end)) which would be reversal([]) which would end up returning the [] unchanged. And you would call reversal(v(1:1)) which would pass the same v into reversal (v must be scalar or the if would not be true), so you would end up calling reversal() with exactly the same input... which is going to call reversal([]) and reversal(v(1)) again which is going to call reversal([]) and reversal(v(1)) again and...

[ghazal]

Thanks friend for your explanation actually I don't get where the problem is, but I changed my code to this and I get this Error!

Error:

Undefined function 'reversal' for input arguments of type 'double'.

Code:

function v = reversal2(v)
if length(v) > 1
    ii=round(length(v) /2 );
    v = [reversal2(v(ii+1:end)) , reversal2(v(1:ii))];
end
end

[Walter Roberson]

You would have a problem running function reversal when the function is named reversal2

Answer 2

[Jeevan]

code run without output

[Walter Roberson]

what code runs without output ?