Find smallest instance satisfying certain inequalities

Question

I need a "clean" way to find the smallest solution to some (in)equalities given by Reduce and containing only one variable x. For example, such an expression could be 1 ≤ x ≤ 2, x == 9 or -1 ≤ x ≤ 4 || 7 ≤ x ≤ 11 || x == 5. I know that FindInstance finds some instance, but I don't know how to restrict the search to the smallest one (it outputs {{x -> 43/34}}, {{x -> 9}} and {{x -> 2/7}} for the previous examples).

In principle, this could be done by using patterns to extract the endpoints of the intervals and choosing the smallest one, but I think there should be a cleaner way.

Answer 1

This is very easily done, using Minimize. Make a list of your examples

conditions = {1 <= x <= 2, 
  x == 9, -1 <= x <= 4 || 7 <= x <= 11 || x == 5}
(* {1 <= x <= 2, x == 9, -1 <= x <= 4 || 7 <= x <= 11 || x == 5} *)

and solve each of them

Minimize[{x, #}, x] & /@ %
(* {{1, {x -> 1}}, {9, {x -> 9}}, {-1, {x -> -1}}} *)