Problem 54730. Local Extrema

Created by Dyuman Joshi

Solve Later

Given a 2D (m,n>1) matrix, replace an element if it is not a local extrema (minima/maxima), with 0 (zero).
The comparison criteria for an extrema should be strict (> or <). (See example #1)
Check the 3 neighbours of the corner points, 5 for elements on the edge and 8 for elements in the middle.
%Example #1
x=[1 2 3
   2 3 1
   3 1 2];
y=[1 0 0
   0 0 0
   0 0 0];
%Example #2
x=[1     4     7    33    12     6    17
  29     8    20    13     3    -1     2
  19    14    26    -8    22    20     4
   1     6     4    17    34    14     2
 -23    27    31     9    30     3    10];
y=[1     0     0    33     0     0    17
  29     0     0     0     0    -1     0
   0     0    26    -8     0     0     0
   0     0     0     0    34     0     2
 -23     0    31     0     0     0     0]
%Example #3
x=[-5   -31   -17    -3   -23   -11
   -2   -37   -19    -7   -13   -29];
y=[0     0     0    -3     0   -11
  -2   -37     0     0     0   -29];
More test cases might be added later.

Solve

Solution Stats

7 Solutions
4 Solvers

Last Solution submitted on Jun 28, 2022

Last 200 Solutions

Problem Comments

6 Comments

6 Comments

Show 3 older comments

ChrisR on 10 Jun 2022

Dyuman, Test 5 is missing a parenthesis.

Dyuman Joshi on 11 Jun 2022

Fixed. It's always something with my test suite :')

William on 11 Jun 2022

Dyuman, Thanks for the problem. It might be good to add that what you mean by a local maximum is not only that the value is the largest value, but also that it is strictly greater than the second largest. Likewise for a local minimum.

Dyuman Joshi on 11 Jun 2022

William, thanks for the comment.

I thought the value of extrema was based on strict criteria. I stand corrected. The problem statement has been updated.

William on 12 Jun 2022

Yes, if this were a continuous function, an extremum would imply that the value was strictly the largest. In the case of a set of discrete values, though, it may be debatable whether two equally large neighbors should be considered as 2 maxima or not.

Dyuman Joshi on 13 Jun 2022

I see, thanks for the clarification!

Solution Comments

Show comments

Problem Recent Solvers4

Problem Tags

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Problem 54730. Local Extrema

Solution Stats

Last 200 Solutions

Problem Comments

Solution Comments

Problem Recent Solvers4

Suggested Problems

More from this Author30

Problem Tags

Community Treasure Hunt

Problem 54730. Local Extrema

Solution Stats

Last 200 Solutions

Problem Comments

Solution Comments

Problem Recent Solvers4

Suggested Problems

More from this Author30

Problem Tags

Community Treasure Hunt

Players