# How to generate a random matrix with a constraint or step range ?

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Varun Pai on 23 Apr 2020
Commented: Varun Pai on 23 Apr 2020
I want to generate a Nx4 random matrix. In this matrix, each column is considered having different range and step. The random values should be only from these steps.
For e.g. 1st column 0:0.1:1
2nd column > 0:1:10
3rd column > 2:0.5:8
4th column > 0:-1:-10
I want to generate a random matrix of N=5. I should get a matrix with above conditions. Like this
[0 5 3.5 -5 ;
0.8 8 7 -3
0.2 0 2.5 -7
0.6 8 6.5 0
0.9 3 7.5 -9]
The N value could go to any size. Repeated values are permissible. I tried some random functions like randperm, randsample etc but I am not able to produce like this. Randperm is not allowing to produce repeated values.
How could I generate it ? Could you help with a code sample ?

KSSV on 23 Apr 2020
Edited: KSSV on 23 Apr 2020
C1 = 0:0.1:1 ;
C2 = 0:1:10 ;
C3 = 2:0.5:8 ;
C4 = 0:-1:-10 ;
N = 5 ; M = 4 ;
C = zeros(N,M) ;
C(:,1) = randsample(C1',5) ;
C(:,2) = randsample(C2',5) ;
C(:,3) = randsample(C3',5) ;
C(:,4) = randsample(C4',5) ;
##### 3 CommentsShow 1 older commentHide 1 older comment
KSSV on 23 Apr 2020
Edited: KSSV on 23 Apr 2020
You split the big number into multiples and pick from each column.
You can use repmat on C1, repeat the values and pick them at once.
Varun Pai on 23 Apr 2020
That's great... Thank you for the suggestion.
function ParameterSet = GenerateRandomSet(MinVal,MaxVal,StepVal,N)
% MinVal : 1 x M array of Lower limit
% MaxVal : 1 x M array of Upper limit
% StepVal : 1 x M array of Step values
% N : ParameterSet row size
% Usage eg. GenerateRandomSet([0 0 2 0],[1 10 8 -10],[0.1 1 0.5 -1],50)
rows = N;
cols = length(MinVal);
ParameterSet = zeros(rows,cols);
for c = 1:cols
ParamVectors = MinVal(c):StepVal(c):MaxVal(c);
repfactor = floor(N/length(ParamVectors)) + 1;
ParamVectors = repmat(ParamVectors,1,repfactor);
ParameterSet(:,c) = randsample(ParamVectors',N);
end
end

madhan ravi on 23 Apr 2020
Hint example:
x = 1:10;
N = 5;
x(randi(numel(x),1,N))

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