Message Boards

7268 Views

3 Replies

3 Total Likes

View groups...

Follow this post

Share this post:

GROUPS:

Mathematics Operations Research Wolfram Language Optimization

Why two optimization problems lead to different results by "MaximalBy"

Posted 5 years ago

Hello, friends Optimization 1: MaximalBy[{{4.9375, {x -> -(3/4)}}, {2.0792, {x -> 2/Sqrt[ 3]}}}, First] the result is: {{4.9375, {x -> -(3/4)}}} Optimization 2: MaximalBy[{{79/ 16, {x -> -(3/4)}}, {-1 + 16/( 3 Sqrt[3]), {x -> 2/Sqrt[3]}}}, First] the result is: {{-1 + 16/(3 Sqrt[3]), {x -> 2/Sqrt[3]}}} Actually, they are the same optimization problems. Why? Thank you very much!

POSTED BY: Shaoyan Robert

3 Replies

Sort By:

Posted 5 years ago

Jim, You must be correct! If you do this, it works as "expected". MaximalBy[{{79/16, {x -> -(3/4)}}, {-1 + 16/(3 Sqrt[3]), {x -> 2/Sqrt[3]}}}, N@*First] (I made the function the Composition of N[] and First[]. so it treats the sort function numerically. Good catch! However, this should be sent to support to improve the documentation and to add an example. Regards, Neil

POSTED BY: Neil Singer

Posted 5 years ago

I think it might be a feature rather than a bug. Consider using `FullForm`: Sort[{{4.9375, {x -> -(3/4)}}, {2.0792, {x -> 2/Sqrt[3]}}, {79/16, {x -> -(3/4)}}, {-1 + 16/(3 Sqrt[3]), {x -> 2/Sqrt[3]}}}, Last] // FullForm So the sorting is lexicographic?