I want to obtain number of cases(matrix's length) . By applying same sum in any matrix. (on constraints)

for example,

A is here.

A=[6 7 8 9];

and,

sumA=sum(A)=30;

The element of the matrix that causes the sum to be 30 must be expressed as a value between 4 and 12.

When I calculate directly, the number of cases that can be obtained is 3,4,5,6,7.

In this way, how to create code?

[Stephen23]

Duplicated here, this thread apparently abandoned by Kyungmin Kim:

https://www.mathworks.com/matlabcentral/answers/356435-how-to-obtain-the-number-of-cases-of-length-but-those-matrices-sum-must-be-30-or-something-value-on

Answer 1

[José-Luis]

If what you mean is that you want the sum of a random array of four elements to be thirty with some condition placed on the last of them:

lims = [4,12];
totVal = 30;
lastElement = randi(diff(lims) + 1,1 ) + lims(1) - 1;
valueToSplit = totVal - lastElement;
frac = rand(1,3);
frac = frac ./ sum(frac);
result = [round(frac.*valueToSplit), lastElement]
sum(result)

Answer 2

[Andrei Bobrov]

z = 4:12;
out = [];
for jj = 1:numel(z)
    k = nchoosek(z,jj);
    out = [out;num2cell(k(sum(k,2) == 30,:),2)];
end

"number of rows":

numel(out)

[Brian Kim]

i don't wanna all cases matrices. I want the number of rows I can get

[José-Luis]

I don't understand what you mean. Could you explain?