How to deal with recursive loop in MATLAB?

Question

I am trying to compute x1^i * x2^j * x3^k * ......

This is my code so far:

for l = 1:N
f = 1;
for i = 0:2
    for j = 0:2-i
        for k = 0:2-j
            for m = 0:2-k
                g(l,f) = x1(l)^i*x2(l)^j*x3(l)^k*x4(l)^m;
                f = f+1;
            end
        end
    end
end
end

How can I do this easier or without a loop?

user827080 · Accepted Answer · 2012-10-07 11:39:48Z

1

I do not have MATLAB on hand here, but what I'd do is make a vector X = [x1, x2, ..., xn] of bases and a vector P = [i, j, k, ..., z] of powers, and then compute prod(power(X, P)).

power() does an element-wise power function, and prod takes the product of every element in the vector.

answered Oct 7, 2012 at 11:39

user827080

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5 Comments

KyungHoon Kim Over a year ago

Answer is that Just Do consist of P. wow thank you so much! but I need recursive loop for P.... T_T

user827080 Over a year ago

I find it really hard to understand exactly what you want to do... :(

KyungHoon Kim Over a year ago

Following your answer, I need to make vectors P. For example, for three variable, p(1)=[0 0 0], p(2)=[0 0 1], p(3)=[0 0 2], p(4)=[0 1 0], p(5)=[0 1 1], p(6)=[0 2 0], p(7)=[1 0 0], p(8)=[1 0 1], p(9)=[1 1 0], p(10)=[2 0 0]. When I calculate many variable(x1, x2, x3, x4, x5, ..., x100), how to make vectors P? maybe I need recursive loop. sorry my poor explanation.. OTL

user827080 Over a year ago

It seems your vector P is the ternary (like binary or decimal, only base 10) representation of the index. Try looking at dec2base.

KyungHoon Kim Over a year ago

Thank you for your help! Your dec2base idea is great!

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