Generate a random signal in Matlab

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Chase Murphy 2019-10-17

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https://ww2.mathworks.cn/matlabcentral/answers/485777-generate-a-random-signal-in-matlab

评论： Steven Lord 2019-10-17

I need to generate a transmit signal of 10,000 random bits in MATLAB with values of -1 or +1, with both having a equal probabilty of occuring and then verify the probability.

I am using y=randi([-1 1],10000)

But I keep getting 0's and do not know how to take them out and am unsure if my function is even correct.

I tried verifying the probabilty by doing 2 different matrices and adding them together and should be equal to 0, but bc i have zeros this did not work.

Any suggestions?

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Answer 1

Daniel M 2019-10-17

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https://ww2.mathworks.cn/matlabcentral/answers/485777-generate-a-random-signal-in-matlab#answer_396711

在 MATLAB Online 中打开

y = (rand(10000,1) > 0.5)*2 -1;

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Adam Danz 2019-10-17

编辑：Adam Danz 2019-10-17

在 MATLAB Online 中打开

To determine the proportion of 1s in y,

p = sum(y==1)/numel(y);

I'll add a 3rd option that requires the Machine Learning Toolbox:

y = randsample([-1,1],10000,true);

Each of these methods have about the same probability of choosing 1. This verification produces 10k values of [-1,1] and it repeats that process 10000 times. It then returns the mean proportions of the value 1 in each iteration.

% number of reps 
n = 10000; 
prob = [0,0,0]; 
fprintf('Testing first method...\n')
tempProb = zeros(1,n); 
for i = 1:n
    y = (rand(10000,1) > 0.5)*2 -1;
    tempProb(i) = sum(y==1)/10000; 
end
prob(1) = mean(tempProb); 
% prob(1) = sum(tempProb==.5);  % alternative
fprintf('Testing second method...\n')
tempProb = zeros(1,n); 
for i = 1:n
    y = randi([0 1], 10000, 1)*2 - 1;
    tempProb(i) = sum(y==1)/10000; 
end
prob(2) = mean(tempProb); 
% prob(2) = sum(tempProb==.5);  % alternative
fprintf('Testing third method...\n')
tempProb = zeros(1,n); 
for i = 1:n
    y = randsample([-1,1],10000,true); 
    tempProb(i) = sum(y==1)/10000; 
end
prob(3) = mean(tempProb); 
% prob(3) = sum(tempProb==.5);  % alternative
%display results
disp(prob)

I was currious about the speed of these methods so I ran each of the (rand, randi, randsamp) 100,000 times. Below are the median execution times and the 95% confidence intervals (percentile method).

Walter Roberson 2019-10-17

在 MATLAB Online 中打开

p = sum(y==1)/numel(y);

for vector y that can be abbreviated to

p = mean(y==1)

for non-vector toss in a (:) after the y or use mean2() instead of mean()

Steven Lord 2019-10-17

在 MATLAB Online 中打开

for non-vector toss in a (:) after the y or use mean2() instead of mean()

You can specify 'all' as the dimension input to mean if you're using release R2018b or newer of MATLAB.

>> A = magic(5);
>> mean(A, 'all')
ans =
    13
>> mean(A(:))
ans =
    13
>> mean(A)
ans =
    13    13    13    13    13

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Generate a random signal in Matlab

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Generate a random signal in Matlab

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