How can I create a for loop inside another for loop for a geometric series?

I have the following code so far:

    %alphaSum.m
    %
    %
    %Amy Wallace, 19/02/2014

    %Variable dictionary
    %N Number of terms to sum
    %alpha Sum of geometric series
    %x vector of constants
    %n Loop counter

    N = input('Enter the number of terms to sum: ');
    alpha = 0;
    x = [0.9 0.99 0.999 0.9999 0.99999 0.999999 0.9999999];
    for n = 0:N-1
        alpha = alpha + (x.^(n));
    end
    format long
    alpha

This allows the user when the script is ran in the command window to enter one term of N to sum. I was wondering, if by using nested looping I could possibly use multiple N terms to sum at the one time? I have already tried calling N as a string with no luck. Thanks

Answer 1

[Mischa Kim]

Amy, check out

Nin = inputdlg('Enter space-separated numbers:', 'N vector', [1 50]);
N   = str2num(Nin{:});

x   = [0.9 0.99 0.999 0.9999 0.99999 0.999999 0.9999999];

alpha = zeros(length(N), length(x));
for ii = 1:length(N)
    for n = 0:N(ii)-1
        alpha(ii,:) = alpha(ii,:) + (x.^(n));
    end
end

[Amy]

This worked great thanks :)