How to create random matrix with specified step in interval [a, b]

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Reza Lashani 2022-5-22

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编辑： Reza Lashani 2022-5-23

Hello everyone. I want to create a matrix with size (m×n) and I want its entities be between 5 and 34 (or in interval [5,34]) with a step of 3. Which means it's only allowed to have 5, 8, 11, 14, ... . How can I create this matrix?

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Answer 1

Voss 2022-5-22

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编辑：Voss 2022-5-22

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a = 5;
b = 34;
step = 3;
offset = 2;
n_levels = 1+floor((b-a)/step)
n_levels = 10
% for your reference, showing the min and max 
% random values that will be generated:
offset + step*[1 n_levels]
ans = 1×2
     5    32
% required size of resulting random matrix:
m = 10;
n = 12;
% generate the matrix using randi,
% [1 n_levels] maps to [5 32]
result = offset + step*randi([1 n_levels],m,n)
result = 10×12
     8     8    11    23    26    23     8    20    20    32    32    26
     5    26    11    20     8    14    11    29    32    23    23    11
    32    20    20    11    23    17    11    17    29     5    23    11
    17     5    11    32    26    14    20     8    11    20    23    20
    26     8    17    20    20    14     8    14    32    14     8    14
    29    32    32    23    17    14    23     8     8    26    29    14
    23    17    23    11    29     8     5    11    26    26    23    26
    17    26    29    17    29    23    17    14    11    20    29    23
    32     8    29    32    20    14    32    26     5     8    17    17
    11    11     5    32    23    14     8     8    20     8    17    17

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Voss 2022-5-22

编辑：Voss 2022-5-22

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Yes it does.

What do you want? 5,8,11,14,17,20,23,26,29,32, and 34? 34 is not 3 more than 32.

If you want 34, please explain how you can achieve that by starting at 5 and going up by steps of 3.

Maybe you meant to say 35?

5:3:35
ans = 1×11
     5     8    11    14    17    20    23    26    29    32    35

If you meant to say 35, set b = 35 in my answer, and it will work:

a = 5;
b = 35;
step = 3;
offset = 2;
n_levels = 1+floor((b-a)/step)
n_levels = 11
% for your reference, showing the min and max 
% random values that will be generated:
offset + step*[1 n_levels]
ans = 1×2
     5    35
% required size of resulting random matrix:
m = 10;
n = 12;
% generate the matrix using randi,
% [1 n_levels] maps to [5 35]
result = offset + step*randi([1 n_levels],m,n)
result = 10×12
    32    23    32    29    35    20    14     8     8    23    26    35
    11    29    32    23     5    17    35    23    17    23    17    14
     5    14     5    32    14    35    26    26    11    14     5     8
    35     5    11    17    14    35     5    29    29     8    23    23
    32    17     8    20    14    11    35     5    20    29    29     8
    20     5    26    20    17    23    26    14    14    11    23     5
    29    20    14    23    35    17    20    26    11    26    35    23
    29    32     5    11    26    23    35    35    17    17    29    32
    17    11    23    17    35     5     5    20    17    17    26    23
    23    35    14    26    17    20    23    23    20    11    29    26

Reza Lashani 2022-5-22

You are correct. Thank you so much 👌🙏

Voss 2022-5-22

You're welcome!

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Answer 2

John D'Errico 2022-5-22

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https://ww2.mathworks.cn/matlabcentral/answers/1724845-how-to-create-random-matrix-with-specified-step-in-interval-a-b#answer_969490

编辑：John D'Errico 2022-5-22

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You can also use indexing. The idea is to generate random indexes.

ValidRandomSet = 5:3:34
ValidRandomSet = 1×10
     5     8    11    14    17    20    23    26    29    32
m = 7;
n = 6;
ind = randi(numel(ValidRandomSet),[m,n])
ind = 7×6
     3    10     4     5     6     7
     5     4     2    10     7     6
     6    10     2    10     8     6
     3     5     1    10     8    10
     7     7     9     6     4     6
     3     3     2     5     9    10
     1     8     9    10     7     3
X = ValidRandomSet(ind)
X = 7×6
    11    32    14    17    20    23
    17    14     8    32    23    20
    20    32     8    32    26    20
    11    17     5    32    26    32
    23    23    29    20    14    20
    11    11     8    17    29    32
     5    26    29    32    23    11

The virtue of such a scheme is it works for any target set of numbers.

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Reza Lashani 2022-5-23

编辑：Reza Lashani 2022-5-23

在 MATLAB Online 中打开

very nice. I could write this by using a foor loop. but your way to doing it, is much better. thank you for your help.

This is what I wrote:

function  out = myfun(Step, a, b, m, n)
    out = zeros(m, n);
    ValidSet = a: Step: b;
    for i = 1: m*n
        ind = randi(length(ValidSet));
        out(i) = ValidSet(ind);
    end
end

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Answer 3

Jonas 2022-5-22

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编辑：Jonas 2022-5-22

在 MATLAB Online 中打开

generate a matrix with random integer values using randi. The spacing will be 1, you can then multiply the values by 3 to get spacing of 3. then shift your values towards your interval by addition

randi(10, 20,30)*3+2

max value will be 32 and minimum value 5

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Reza Lashani 2022-5-22

编辑：Reza Lashani 2022-5-22

Thank you so much 👌

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Answer 4

Image Analyst 2022-5-22

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https://ww2.mathworks.cn/matlabcentral/answers/1724845-how-to-create-random-matrix-with-specified-step-in-interval-a-b#answer_969470

在 MATLAB Online 中打开

Here's another way. You can create your random numbers as floating point then use discretize them into numbers in the set you specify:

m = 6
n = 18
% Get the random numbers
r = 5 + (35-5) * rand(m, n)
% Discretize into nearest integer that is in the set 
% [5    8    11    14    17    20    23    26    29    32]
edges = 5:3:35
values = edges(1:end-1)
r2 = discretize(r, edges, values)

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Reza Lashani 2022-5-22

It is a very nice method. Thank you

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How to create random matrix with specified step in interval [a, b]

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