Matlab - Dos ficheros simples que me dan error

function [factors]=opcional5(x)

p = primes(x);

lp = length(p);

for i = 1:lp

    if rem(x,p(i)) ~= 0

    p(i) = [];

    end

end

factors = p;

function [xf] = opcional4(x)

t = x;

n = length(t);

xf=zeros(1,n);

for i = 1:n

    if t - t(i) >= 0

        for k = 1:n

            v(k)=t(i);

            t(i) = [];

        end

    end

end

function factors=opcional5(x)

if nargin==0

    x=24;

end

p = primes(x);

lp = length(p);

k=1;

for i = 1:lp

    if rem(x,p(i)) == 0

    P(k) = p(i);

    k=k+1;

    end

end

n=1;

for i=1:length(P)

    cond=0;

    while cond==0

         if rem(x,P(i)) == 0

             x=x/P(i);

             f(n)=P(i);

             n=n+1;

         else

             i=i+1;

             cond=1;

         end

    end

end

factors = f;

end

>> x=24, factors=opcional5(x)

x =

    24

factors =

     2     2     2     3

>> x=36, factors=opcional5(x)

x =

    36

factors =

     2     2     3     3