Find a function from a Recursive Formula

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Discussion Overview

The discussion revolves around finding a function \( W_{t}^{x} \) from a recursive formula related to a one-armed bandit problem involving a Bernoulli probability \( \theta \). The participants explore the implications of the recursive relationship and the expectations involved.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant presents the recursive formula for \( W_{t}^{x} \) and asks for suggestions on solving it.
  • Another participant questions the variable with respect to which the expectation is taken and the range of integration, suggesting it might be over \( \theta \) from \(-\infty\) to \(\infty\).
  • Concerns are raised about the recurrence rule for \( W \), specifically that "x" does not decrease, leading to questions about the initial values needed for the recursion.
  • A clarification is made that the expectation is indeed with respect to \( \theta \), which is defined on the interval \([0,1]\).
  • The original poster expresses a need to determine the initial value \( W^{0}_{0} \) or \( W^{x}_{t} \) as part of solving the problem.

Areas of Agreement / Disagreement

Participants express uncertainty regarding the initial values required for the recursive formula and the specifics of the expectation involved. No consensus is reached on how to proceed with determining the initial values.

Contextual Notes

The discussion highlights limitations regarding the assumptions about the initial values and the dependence on the definitions of the variables involved in the recursive formula.

loveinla
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Hi,

I'd like to solve a function W_{t}^{x} from a recursive formula below.

W_{t}^{x}=P_{t}^{x}*W_{t+1}^{x+1}+(1 - P_{t}^{x})*W_{t+1}^{x},

where P_{t}^{x} = \frac{E[\theta^{x+1}*(1 - \theta)^{t-x}]}{E[\theta^{x}*(1-\theta)^{t-x}]}, {\underset{t\to\infty, x\to 0}{lim}}W_{t}^{x} =0. Here E stands for expectation.

Any suggestions? Thanks.
 
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loveinla said:
E stands for expectation.

Expectation with respect to which variable? Over what range of integration?
 
Stephen Tashi said:
Expectation with respect to which variable? Over what range of integration?
I'd imagine on the only free variable in the expression for P, namely \theta, and over (-\infty,\infty). But you do well in asking instead of guessing like yours truly. :)

What worries me most is that, in the recurrence rule for W, the "x" does not get any smaller. So what are supposed to be the initial values?
 
dodo said:
I'd imagine on the only free variable in the expression for P, namely \theta, and over (-\infty,\infty). But you do well in asking instead of guessing like yours truly. :)

What worries me most is that, in the recurrence rule for W, the "x" does not get any smaller. So what are supposed to be the initial values?

Thanks, you are right, the expectation is with respect to \theta, which is on [0,1].

The initial value is indeed what I am trying to find.

In fact, it is a one-armed bandit problem with Bernoulli probability \theta, but \theta is a random variable we are trying to figure out through the realization.

Any idea on how to determine the initial value W^{0}_{0} or W^{x}_{t}?
 

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