random number generation to add and subtract

Question

Ananya Malik 2017-9-8

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https://ww2.mathworks.cn/matlabcentral/answers/355708-random-number-generation-to-add-and-subtract

回答： Guillaume 2017-9-8

I want to create an array of 4 single digit numbers in the range [-9,9] without 0. Addition of these 4 numbers should result in a positive number within 0-9 range. for ex. a= [4,-2,3,-1] =4. However 1st number should be compulsorily positive. And subsequent addition/subtraction should be valid.(i.e. negative number should be subtracted from a positive number). Any help would be greatly appreciated.

So far I have tried this:

a= randi([-9,9],4,1);
    if sum(a)>=0 && sum(a)<9         
        a'
    end

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Pal Szabo 2017-9-8

What you mean by this? "And subsequent addition/subtraction should be valid.(i.e. negative number should be subtracted from a positive number)."

Ananya Malik 2017-9-8

4-2 = 2. this 2+3(3rd number in array) = 5; 5 -1(last number in array) = 4. It means intermediate results should be positive.

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Answer 1

Pal Szabo 2017-9-8

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在 MATLAB Online 中打开

Try this, it works for me.

 % invoke myfunction
 [firstnum secondnum thirdnum fourthnum]=myfunction
 % if the fourth number produced is outside the desired range or zero,
 % invoke function again
 while (-9<=fourthnum & fourthnum<=9 & fourthnum~=0)==0
    [firstnum secondnum thirdnum fourthnum]=myfunction
 end
 %%here are your numbers
 firstnum
 secondnum
 thirdnum
 fourthnum
 function [firstnum secondnum thirdnum fourthnum]=myfunction
 base1  = [-9:1:-1];
 base11 = [1:1:9];
 base = [base1 base11];
 i=randi(9);
 firstnum=base11(i);
 ii=randi(18);
 secondnum=base(ii);
 iii=randi(18);
 thirdnum=base(iii);
 fourthnum=4-firstnum-secondnum-thirdnum
 end

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Answer 2

KL 2017-9-8

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https://ww2.mathworks.cn/matlabcentral/answers/355708-random-number-generation-to-add-and-subtract#answer_280749

编辑：KL 2017-9-8

在 MATLAB Online 中打开

numsum = -1;
while numsum<0 || numsum>9
     a = randi([1 9]);
    b = randi([-9 9],3,1);
    while b(1)==0 || b(2)==0 || b(3)==0
        b = randi([-9 9],3,1)
    end
    num = [a;b];
    numsum = sum(num);
end

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Answer 3

Guillaume 2017-9-8

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https://ww2.mathworks.cn/matlabcentral/answers/355708-random-number-generation-to-add-and-subtract#answer_280755

在 MATLAB Online 中打开

Another option:

numbers = -1;
while sum(numbers) < 0 | sum(numbers) > 9 | any(cumsum(numbers) < 0)
   numbers = randi([1 9], 1, 4) .* (-1).^[2, randi([1 2], 1, 3)];
end