# Huge matrix with Nchoosek

9 views (last 30 days)
Hamad Gul on 13 Sep 2019
Commented: Vahid Hamdipoor on 23 Mar 2020
I have a program where I need all possible combinations between two variables(N and T). Facing "Out of Memory" problem whenever T increases 4. Is there any solution for this?
clear;
% spiky signal generation
N = 255; %maximum users
T = 10; % number of spikes
a = zeros(N,1); %creating N-by-1 all zero vector
C = nchoosek(1:N,T); %creating all the combination values between N and T
e= nchoosek(N,T); %number of all possible combinations
x0 = zeros(N,1); %creating N-by-1 all zero vector
count = 0; %used in calculating success
%disp(C);
for K = 1:1:N %K, m are two variables to identify the element in C
a = zeros(N,1); %creating N-by-1 all zero vector
for m = 1:1:T; %used to initiate loop for reading the elements in C
i= C(K,m);
a(i) = 1; %i defining the place of 1 in all zero vector a
x0(1:N)=a; %putting x0 as a
end
if a(i) ~= 0; %implementing network conditions
n = randn(1,1); % white gaussian noise, 0dB variance
h = 1/sqrt(2)*[randn(1,1) + j*randn(1,1)]; % Rayleigh channel
h_abs = abs(h);
x0(i) = 1 * h_abs + 10^(-1/1)*n;
y = HD2255*x0; % measurements with no noise
lambda = 0.0001; % regularization parameter
rel_tol = 0.01; % relative target duality gap actual 0.01
[x,status]=l1_ls(HD2255,y,lambda,rel_tol);
for s = 1:size(x0,1); %starting a loop to calculate success
for t = 1:size(x0,2);
if x0(s,t) ~= 0; %when x0 is avtive
d(s,t) = abs(x0(s,t)) - abs(x(s,t)); %difference
if d(s,t) < 0.1; %success criteria
count = count + 1; %counting the number of times it is successful
% cnt = count / e
%perc = (cnt*100)/T
% sta(s,t) = -1;
%else sta(s,t) = 1;
%fprintf('count\n', count)
disp(count);
end
end
end
end
end
end
%end
cnt = count / e
perc = (cnt*100)/T
Rena Berman on 19 Sep 2019

Bruno Luong on 13 Sep 2019
Edited: Bruno Luong on 13 Sep 2019
You became real "Patient" now? Good! Then run this look at the screen and wait until it stops. If your type Ctrl C or kill MATLAB or reboot your PC, etc.., you must come back and change your claim ;-)
seq_nchoosek(255,10); % function bellow
while true
c = seq_nchoosek(); % function bellow
disp(c)
if size(c,1)==0
break
end
% ... do your stuff with c
end
(Put function in seq_nchoosek.m mfile)
function v = seq_nchoosek(n,k)
% Sequential NCHOOSEK
% N and K non negative integers k <= n
% seq_nchoosek(n,k) % reset the sequence of combination
% v = seq_nchoosek() % query the next combination
%
% % Exemple of calling sequence:
% seq_nchoosek(5,3)
% while true
% c = seq_nchoosek()
% if size(c,1)==0
% break
% end
% % ... do something with c
% end
%
persistent V S I K
if nargin >= 2
% reset
if ~(isscalar(n) && isscalar(k))
error('seq_nchoosek: n and k must be scalars');
end
if k > n
error('seq_nchoosek: k must be smaller or equal to n');
end
if n == 0
V = [];
else
k = floor(k);
n = floor(n);
if n < 0 || k < 0
error('seq_nchoosek: n and k must non negative integers');
end
V = 1:k;
I = k;
K = k;
S = V+(n-k);
end
end
if nargout >= 1
% query
v = V;
if size(V,1) > 0
% move to next
I = find(V-S,1,'last');
if ~isempty(I)
V(I) = V(I)+1;
V(I+1:K) = V(I)+(1:K-I);
else
V = [];
end
end
end
end
Vahid Hamdipoor on 23 Mar 2020
@Bruno Luong Thank you so much. This is a great piece of code, And it solved my problem as well.

R2019a

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