I am an economist with some math background but not strong enough to solve this. I'm trying to solve

Aganippe76

Aganippe76

Answered question

2022-07-12

I am an economist with some math background but not strong enough to solve this. I'm trying to solve:
max x   f ( x , y ( x ) ) = a y ( x ) + b g ( x )
where
y ( x ) = 1 ( h ( x ) > 0 ) .
h ( x ) is a linear function of x and a , b R are constants. x X and X is a compact and continuous subset of [ 0 , 1 ]. g ( x ) is a concave and differentiable function.

Now, my problem is that the optimal choice of x depends on the value of y( x), which depends on x.

I would like to know how to solve for, if possible, a closed-form solution. If it is impossible, what kind of algorithm should I use, and where can I find the essential readings to learn them.

EDIT: Thanks Robert for his great answer. Now I would just like to ask this follow-up question:

Can this method of solving for the maximum be adopted in a dynamic programming version of this problem? Say I want to maximise V ( x t ) = max x t f ( x t , y t ( x t ) ) + δ V ( x t + 1 ) but the constant a now becomes a function of x t 1 ? δ is a discount factor.

Answer & Explanation

Amir Beck

Amir Beck

Beginner2022-07-13Added 13 answers

Essentially there are two separate problems to consider:

1. maximize b g ( x ) on { x : h ( x ) 0 }.
2. maximize a + b g ( x ) on { x : h ( x ) > 0 }.

and then you take whichever of these solutions has the best objective value. To complicate matters, however, there is no guarantee that a maximum is attained in (2), as { x : h ( x ) > 0 } is not closed. If a > 0 and the maximum of a + b g ( x ) on { x : h ( x ) 0 } occurs only at a point where h ( x ) = 0, the problem does not have an optimal solution.

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