if i have a i*j matrix(with random numbers ), then how can i make the sum of first row = d(say d= 5).

HELLO,

I want to make random number matrix having the sum of first row elements equal to d (a positive number). I tried to use Roger Stafford's randomfixedsum for first row but was not successful.

thank you

Resh

[Ben11]

Can you please show the code you actually used that did not work?

Answer 1

[Orion]

You can do this: http://www.mathworks.com/matlabcentral/newsreader/view_thread/318632 And you don't need a value constraint in the first line.

Answer 2

[Aykut Satici]

I understand that you would like to get a matrix A with m rows and n columns, and your constraint is that the first row has to sum to d

This means you can arbitrarily select (n-1) of these numbers such that their sum is less than d and then assign the last one such that the whole sum is d.

As a result, one way of doing this would be to generate (n-1) random numbers all of which is smaller or equal to d/(n-1) and then select the last one as d minus the sum of the previous (n-1). See the code below:

m = 4;      % number of rows
n = 7;      % number of columns
d = 5;      % desired sum of the first column
a = 10/17;   % lower bound on the elements of the first row of A

% Generate the matrix
A = zeros(m,n);                             % Create a matrix of zeros
                                            % of dimension m-by-n
A(2:m,:) = rand(m-1,n);                     % Populate the elements of the
                                            % matrix through rows 2 to m
                                            % with random numbers
A(1,1:n-1) = a + (d/(n-1)-a)*rand(1,n-1);   % Generate (n-1) random numbers
                                            % between a and d/(n-1)
                                            % (see "help rand")
A(1,n) = d - sum(A(1,1:n-1));

[reshdev]

Hello Sir, thank you for your valuable response. Actually, i am new to matlab programming.So, i don't know much programming. can you please modify the above program such that all the elements in resultant matrix should be >=0.

thank you

Actually,the main problem is...............(if you can help me for this)

Please help me to write matlab code, I am trying to create 5*5 matrix containing random values having constraints....... (1) sum of elements of row 1(X1) = sum of elements of column 1 (X1) (Sum = X1<= 7)............. (2) sum of elements of row 2 =7 and sum of elements of column 2 = 0 .......... (3) sum of elements of row 3(X3) = sum elements of column 3(X3) (Sum X3 <= 7)............ (4) sum of elements of row 4 =0 and sum of elements of column 4 = 7 ................ (5) sum of elements of row 5(X5) = sum elements of column 5(X5) (X5<= 7)........

Rows act as sources nodes. columns act as destination nodes.

Actually, this matrix represents a transshipment problem which is sending 7 units of data from (starting node 2) to (termination node 4).above constraints show that data going into node 2 from all nodes is zero and going out to all nodes is 7 units. Similarly, data going into destination node 4 is 7 units and nothing comes out from this. Whereas for all the other nodes, total amount of data coming in = total amount of data coming out.

all the diagonal elements should be zero. like (1,1)...(2,2).....(5,5) and range for all elements of matrix = 0 to 7

This is what i am able to do so far....

no_sourcenode = input ('ENTER THE NUMBER OF source NODE :');

no_destiantion = input ('ENTER THE NUMBER OF destination node :');

chromosome = round(rand(no_sourcenode,no_destiantion));

chromosomes(1:(no_sourcenode+1):no_sourcenode*no_destiantion)= 0; (to make diagonal elements zero)

Thank you very much

Resh

[Guillaume]

What you're asking now is completely different from what you've asked originally. You should create a new question.

Answer 3

[Guillaume]

You don't say what you want to happen in the other rows, so I would just generate a random matrix, divide it by the sum of the first row and multiply it by d.

M = rand(nrows, ncols);
M = M / sum(M(1, :)) * d;

[reshdev]

ok great. Thank you again. Now, you can have a look at my main problem. i have mentioned constraints that represents different sums for different rows and columns. I have also written a small program at the end. After that, i was unable to do anything.

Can you please take a look at that one too. It will be highly appreciated.