how, using a for loop, can I create an array

I am trying to create an array for V and A that can then be plotted.

for a = [.25:.25:4] %innder radius
b = a+2 ;%outer radius
V = (.25*pi^2).*(a+b)*(b-a).^2 %equation for Volume
A = pi^2*(b^2-a.^2) %equation for Area
end
plot(V,A) %plot Volume vs. Area

with the current code, when I run the script, V and A only have one value which is equal to using a = 4

but I want every value to be saved, not just the last value for V and A

Answer 1

[per isakson]

how using a for loop

V and A are overwritten for every iteration of the loop. Try this

vec = [.25:.25:4];
len = length( vec );
A = nan( len, 1 );
V = nan( len, 1 );
for jj = 1 :  len
    a = vec(jj);
    V(jj) = (.25*pi^2).*(a+b)*(b-a).^2 %equation for Volume
    A(jj) = pi^2*(b^2-a.^2) %equation for Area
end
plot(V,A) %plot Volume vs. Area

Answer 2

[David Hill]

No loop needed.

a=.25:.25:4;
b=a+2;
V=(.25*pi^2).*(a+b).*(b-a).^2;
A=pi^2*(b.^2-a.^2);
plot(V,A);

[George Amor]

This is much simpler than a for loop, thank you