Mathematics for Economists

(Greg DeLong) #1

Optimal control, minimum problems


One can handle a minimum problem by changing the sign of the goal
function. The Hamiltonian is

H=f+pg, dp
dt

=Hx^0 =(fx+pgx).

Multiplying by1 and introducingep=p

dp
dt

=(fx+pgx), dep
dt

=(fx+epgx)=Hex^0.

That isepis an solution of the adjoint equation of the maximum problem.
Zt 1
t 0

fdt!max, x=g.

u(t)is maximizingH=f+pg=(f+epg)and therefore there
is solutionepof the adjoint equation for whichu(t)is minimizing the
HamiltonianH=f+epg. In this case one can talk about a minimum
principle.
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