How can I call the first value from a for loop into a vector?

After the for loop runs, I need to create a vector that displays all of the output from the for loop along with the first value of each variable (a=0 & b=1). How can I add the first value of a and b to the beginning of the vector?

a = 0;
b = 1;
for i = 1:20
    c = a+b; 
    a = b; 
    b = c; 
    q(i) = c;
end
vec = q;

Answer 1

[James Tursa]

Remember the starting values prior to the loop. E.g.,

A = a;
B = b;

Then after the loop concatenate:

vec = [A,B,q];

To avoid inadvertently including the q values from past runs, pre-allocate q prior to the loop. E.g.,

n = 20;
q = zeros(1,n);
for i = 1:n
     :

There are also ways to do this using only one vector and doing everything with just indexing, avoiding the a = b and b = c stuff. E.g., an outline

n = 20;
vec = zeros(1,n);
vec(1) = 0;
vec(2) = 1;
for i=3:n
    vec(i) = __________; % some expression of previous vec values
end

I will leave it to you to figure out what goes in the blank above.

[Devon Von Lichtenstein]

Thank you!

Answer 2

[Peter]

This seems like a homework question, so I won't give you complete code for it, but I will give you a few hints. If you want an array at the end, you will want to initialize q to how wide you want. Something like

q= [0 0 0];

Then you can append the values that you want on the end of that array with each iteration. Something like

q = ([q; a b c]);

If you want a cell array, then you could just do

q{i} = [a b c];

With each iteration.