Recall that the exponential distribution with parameter \lambda is given by the pdf by

\displaystyle \displaystyle f_\lambda (y) = \lambda e^{-\lambda y}.
Let \theta =\lambda. Rewrite f_\lambda (y) in the form

\displaystyle \displaystyle f_\theta (y) = h(y) \exp \left( \eta (\theta ) T(y) -B(\theta ) \right),
and enter \eta (\theta ),\, T(y),\, B(\theta ) below.

These functions are not unique. To get unique answers, let h(y)=1,\, and let the coefficient of y in T(y) be +1.

T(y)=\quad
unanswered

\eta (\theta )=\quad
unanswered

B(\theta )=\quad
unanswered

If instead of h(y)=1,\, we had used \widetilde{h}(y)=C for some constant C, then what is \widetilde{B}(\theta ) in terms of B(\theta ) and C? That is, find \widetilde{B}(\theta ) such that the pdf f_\theta (y) of Y\sim \textsf{Exp}(\theta ) is

\displaystyle \displaystyle f_\theta (y) \, =\, \widetilde{h}(y) \exp \left( \eta (\theta ) T(y) -\widetilde{B}(\theta ) \right).
(Enter B for B(\theta ) and C for C.   Your answer should be in terms of only C and B(\theta ). Enter “ln" for the natural logarithm.)

\widetilde{B}(\theta )=\quad

1 answer

T(y) = y
η(θ) = -1/θ
B(θ) = 0

If h(y) is replaced by h̃(y) = C, then the new B̃(θ) can be found by:

B̃(θ) = B(θ) - ln(C)