How to prove that a gaussian rv multiplied by a sine also guassian ?

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Discussion Overview

The discussion revolves around the question of whether a Gaussian random variable multiplied by a deterministic sinusoidal function results in another Gaussian random variable. The scope includes theoretical considerations of stochastic processes and Gaussian distributions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant asks how to prove that a Gaussian random variable multiplied by a sinusoid results in a Gaussian random variable.
  • Another participant points out the ambiguity in the question, questioning how the times for sampling the random variable B are chosen.
  • A participant states that B is a stochastic process that is Gaussian for each time t.
  • A later reply suggests that at a specific time t, the sinusoid acts as a constant, and multiplying a Gaussian random variable by a constant yields another Gaussian random variable.
  • Another participant agrees with this reasoning but emphasizes that a more detailed proof is necessary to establish that B is a Gaussian process, referencing a Wikipedia article on Gaussian Processes.

Areas of Agreement / Disagreement

Participants generally agree on the nature of the relationship between Gaussian random variables and constants, but there is no consensus on the proof that B is a Gaussian process, as the discussion remains unresolved regarding the specifics of the sampling method and the implications for the Gaussian nature of B.

Contextual Notes

The discussion highlights the need for clarity regarding the sampling method used for the stochastic process B and the conditions under which the Gaussian nature is maintained. There are unresolved aspects related to the definitions and assumptions about the sampling times.

dexterdev
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How to prove that a gaussian random variable multiplied by a deterministic sinusoid also results in a random variable with gaussian pdf?

Suppose here A is a guassian random variable and B is given as below where fc is the frequency of sinusoid and t is the time.

B=A∗cos(2π fc t). Is random variable B also gaussian. If so, how to prove it?

This may be a foolish question and/ or direct one . But please help me, I cannot figure it out.
 
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It isn't a foolish question, but it is an ambiguous question. When you take random samples from B, how are you picking the times at which to take these samples? For example, are you sampling B every 10 seconds? Or are you selecting the times to take the samples from some probability distribution?
 
B = B(t) is a stochastic process, which is Gaussian for each t.
 
Stephen Tashi said:
It isn't a foolish question, but it is an ambiguous question. When you take random samples from B, how are you picking the times at which to take these samples? For example, are you sampling B every 10 seconds? Or are you selecting the times to take the samples from some probability distribution?

Hi Sir, I believe that I have figured it now. Please correct me if I am wrong. When considering random processes (independent variable is time t, right?) we consider an ensemble of random waves (of same experiment). So at a particular 't = T' sinusoid is a constant and a constant times gaussian rv is again gaussian. Is this right?
 
dexterdev said:
So at a particular 't = T' sinusoid is a constant and a constant times gaussian rv is again gaussian. Is this right?

That is correct, as mathman pointed out. But if you are trying to write a proof that B is a gaussian process you should say more. For example, in the Wikipedia article on Gaussian Process, note the line:

More accurately, any linear functional applied to the sample function Xt will give a normally distributed result
 
Thankyou Sir
 

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