MATLAB adding noise into data

add percent  % noise to each value
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percent=.03;

sample = sampleMatrix(index, :);
noiseSample=[];
for i=1 :instanceSize
       val = sample(i);
       smallPerc = val * percent ; % 1 percent noise add
       noise = smallPerc* [ rand(1) - 0.5 ]; % .*T
       noisyVal = val + noise ; % small is very small 10e-9
       noiseSample = [noiseSample noisyVal];
end
noiseMatrix = [ noiseMatrix ; noiseSample];

Add little noise to X
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X 
rand( 'state', 0 ) % any number for random number
randn('state', 0 ) % any number for random number
small = 10e-11
small* [ rand(size(X)) - .5 ] .* X + X  % small is very small 10e-9
index = ceil(a + (b-a).*rand(1) ); %