I am trying to generate random numbers between 1 and 5 using Matlab's randperm and calling randperm = 5.
Each time this gives me a different array let's say for example:
x = randperm(5)
x = [3 2 4 1 5]
I need the vector to be arranged such that 4 and 5 are always next to each other and 2 is always between 1 and 3... so for e.g. [3 2 1 4 5] or [4 5 1 2 3].
So essentially I have two "blocks" of unequal length - 1 2 3 and 4 5. The order of the blocks is not so important, just that 4 & 5 end up together and 2 in between 1 and 3.
I can basically only have 4 possible combinations:
[1 2 3 4 5]
[3 2 1 4 5]
[4 5 1 2 3]
[4 5 3 2 1]
Does anyone know how I can do this?
Thanks
You can generate each block and shuffle each one then and set them as members of a cell array and shuffle the cell array and finally convert the cell array to a vector.
b45=[4 5]; % block 1
b13=[1 3]; % block 2
r45 = randperm(2); % indices for shuffling block 1
r13 = randperm(2); % indices for shuffling block 2
r15 = randperm(2); % indices for shuffling the cell
blocks = {b45(r45) [b13(r13(1)) 2 b13(r13(2))]}; % shuffle each block and set them a members of a cell array
result = [blocks{r15}] % shuffle the cell and convert to a vector
I'm not sure if you want a solution that would somehow generalize to a larger problem, but based on how you've described your problem above it looks like you are only going to have 8 possible combinations that satisfy your constraints:
possible = [1 2 3 4 5; ...
1 2 3 5 4; ...
3 2 1 4 5; ...
3 2 1 5 4; ...
4 5 1 2 3; ...
5 4 1 2 3; ...
4 5 3 2 1; ...
5 4 3 2 1];
You can now randomly select one or more of these rows using randi, and can even create an anonymous function to do it for you:
randPattern = @(n) possible(randi(size(possible, 1), [1 n]), :)
This allows you to select, for example, 5 patterns at random (one per row):
>> patternMat = randPattern(5)
patternMat =
4 5 3 2 1
3 2 1 4 5
4 5 3 2 1
1 2 3 5 4
5 4 3 2 1
