1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Binary Hypothesis test

  1. Nov 10, 2009 #1
    1. The problem statement, all variables and given/known data

    This was a midterm question that took some people a rapid time to solve, hence I can only imagine either I was needlessly long winded or something else occurred.

    Hypothesis 1: [tex]S = 2 + \omega[/tex]
    Hypothesis 2: [tex]S = -2 + \omega[/tex]
    [tex]\omega \sim \mathcal{N}(0,\sigma^2_{w})[/tex]


    2. Relevant equations

    The following observations are made:

    diag.jpg

    [tex]N_1 \sim \mathcal{N}(0,\sigma^2_1)[/tex]
    [tex]N_2 \sim \mathcal{N}(0,\sigma^2_2)[/tex]

    Formulate the likelihood ratio test


    3. The attempt at a solution

    Clearly, the variable [itex]S[/itex] has its conditional PDF shifted about the respective mean, and so I yield the likelihood ratio as follows:

    [tex]
    \vec{r} \triangleq
    \begin{pmatrix}
    r_1\\
    r_2
    \end{pmatrix}
    [/tex]

    [tex]

    \Lambda(\vec{r}) = \exp(-\frac{1}{2}((\vec{r} - \vec{\mu_{H1}})^{T} \mathbb{R}^{-1}(\vec{r} - \vec{\mu_{H1}}) - (\vec{r} - \vec{\mu_{H0}})^{T} \mathbb{R}^{-1}(\vec{r} - \vec{\mu_{H0}})))

    [/tex]

    Where

    [tex]
    \vec{\mu_{H1}} =
    \begin{pmatrix}
    2\\
    0
    \end{pmatrix}
    [/tex]
    [tex]
    \vec{\mu_{H0}} =
    \begin{pmatrix}
    -2\\
    0
    \end{pmatrix}
    [/tex]

    and

    [tex]
    R =
    \begin{bmatrix}
    \sigma_1^2 + \sigma_{w}^2 & \sigma_1^2\\
    \sigma_1^2 & \sigma_{1}^2 + \sigma_2^2
    \end{bmatrix}
    [/tex]


    Clearly the issue here becomes a matter of algebraic reduction after taking the natural logarithm. I have omitted any 'threshold' on the RHS (Bayes criterion for example).

    Is this formulation correct thus far? Some people mentioned no need for matrix inversions of any type....Can this problem be simplified or have I needlessly made things difficult for myself?

    With thanks,

    :)
     
  2. jcsd
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?



Similar Discussions: Binary Hypothesis test
Loading...