Adding all possible combinations of array elements

I have an array of elements,

How would I generate a new array of all possible combinations, multiples, and combinations of multiples within a threshold limit of, say, 30?

ex:

X=[a b c d]; where a, b, c, d are real, positive, small integers

M=[a, b, c, d, 2*a, 2*b, ... 3*a, 3*b,...4*a, 4*b, ...a+b, a+b+c,... 2a+2b,...2a+c,... 10a+10b+d, ... .. .. ]

M(M>=30)=[];

where ALL possible combinations are there, excluding repeat combinations, but including repeat numbers

[Image Analyst]

Well I think that would be an infinite number of numbers, unless you put on some constraints, like the multiplication factors must be positive integers or something.

Is this homework? It kind of sounds like homework.

And do you need to keep track of the multiplication factors that were used to create each number?

[Image Analyst]

Hey, are you still there?

[K]

Hey, I'm still here. It's not homework, it is a simulation program to help model data.

There are definitely constraints. They are all positive, real numbers, that have larger spacing between them as I to the right on the array. I don't need to keep track of the multiplication factor as I go.

I was thinking to first make a matrix of the multiplication factors, where I have my array accross the top line, then all the multiples below, then deleting the numbers greater than my limit. Like so:

a b c d

2a 2b 2c 2d

3a 3b.....

Then doing all the number combinations after that... ?

Answer 1

[Ahmet Cecen]

Use combnk to get the the unique combinations over a,b,c and d. For each of those combinations, use base math to get the repetitive variations from 1 to 30. However, the number of elements within M might explode at 30. You might want to consider a lower number.

[K]

Thank you. Using combnk is working great, the only problem is, is that I want to sum across the rows of each combnk matrix I am generating for different sizes. My coding, is like so:

for k=2:4

    C = combnk(B,k);

    C1=sum(C,2);

    C1(C1>E_avail)=[]

end

Here, B is an array. when I step through the loop, everything looks right. But I want to keep the data, so I tried making C into C(k). This gives me the error message:

"In an assignment A(I) = B, the number of elements in B and I must be the same."

Is there a good way to do this?

[Ahmet Cecen]

Use cell structure to keep the C's. C{i} with curly brackets.

[K]

This gives me the error:

"Cell contents assignment to a non-cell array object."

Is there another way?

[K]

Actually, i just got it working. Thank you for your advice. The curly brackets work wonderfully. I just had to create a cell array outside the for loop for it to input into.