I do not understand what is your exact problem. 

I think that your code will be more efficient if you remove de loop for.

Try this

v=0:.1:25;

rho=1.23;

A=8459;

p=.5*rho*A*(v.^3)

plot(v,p, 'r')

xlabel('velocity(m/s)')

ylabel('power(kw)')

v=0:.1:25;

rho=1.23;

A=8459;

for i=1:length(v)

p(i)=.5*rho*A*(v(i).^3)

end

plot(v,p, 'r' 3)

legend('velocity(m/s)', 'power(kw)')

I do not understand what is your exact problem. 

I think that your code will be more efficient if you remove de loop for.

Try this

v=0:.1:25;

rho=1.23;

A=8459;

p=.5*rho*A*(v.^3)

plot(v,p, 'r')

xlabel('velocity(m/s)')

ylabel('power(kw)')

but what if Cp value is also random variable then there will be more than one random variable in equation.