How do i add normal error to some ideal values ?

Hello,

I have a set of ideal -error free- measurements and i want to add some error to them to simulate measurement error (noise etc). I want to know how to add an error with a known standard deviation.

X is the ideall measurements. σ is the standard deviation of the error measurement - known e - error

Xreal = X + e

Xreal = X + σ^2*randn(1) ?

this is not right becouse i will have only positive errors...

please help needed!!

Answer 1

[Wayne King]

Assume x is your error-free data

    x = cos(pi/4*(0:99));
    % now add the error, let the standard deviation be 2
    x = x+ 2*randn(size(x));

You do not want to multiply randn() by the variance, you multiply by the standard deviation.

[Valeriu]

Thanks a lot for the answer!!

[ANetTow]

Is there any difference between using randn as above or using random? For example, using the same items from above:

x = random('norm', x, 2);