# Random numbergeneration with constraints

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Lusine on 5 Jul 2012
Hi,
I want to generate a random matrix, with two constraints 1.the sum of each row of the matrix is less or equal to let's say 60. 2.And the values must be within a specified range, say between 10 and 20.
Can anyone help me with this?
Thank you so much for your help!

Tom on 5 Jul 2012
ulim=20; %max value
llim=10; %min value
rowlim=60; %max sum for each row
m=5; %rows
n=4; %columns
RMat=rand(m,n)*(ulim-llim)+llim;
Rsum=sum(RMat,2);
Rcheck=Rsum>rowlim;
while any(Rcheck) %replace any row whose sum is > rowlim
I=find(Rcheck);
RMat(I,:)=rand(length(I),n)*(ulim-llim)+llim;
Rsum=sum(RMat,2);
Rcheck=Rsum>rowlim;
end
disp(RMat)
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Lusine on 7 Jul 2012
Thanks! It was a great help for me!

### More Answers (2)

Nirmal on 5 Jul 2012
What happens if number of columns is something large may be 20? it would definitely cross your constraint of 60. if you plot the histogram of random numbers every number are equally likely. if you set the number of columns to be within certain limit based on your limit on the sum you can achieve what you are looking for, otherwise the number you will generate will not be random.

Walter Roberson on 6 Jul 2012