Combinatorial optimization problems

9 important questions on Combinatorial optimization problems

Give the approach for the Hungarian method

Step 1
  • Find the minimum in each row;
  • Substract the minimum from each value in each row;
  • Find the minimum in each column;
  • Substract the minimum from each value in the column;

Step 2
  • Draw a minimum number of lines needed to cover all the zeros;
  • m lines required? Optimum solution is found among the 0's
  • <m lines? Continue step 3


Step 3
  • Find the smallest non zero element not covered by lines k;
  • Substract k from each uncovered element;
  • Add k to each element that is covered by 2 lines;
  • Go back to step 2;

Give the steps to execute MST

Step 1
  • Begin at note i
  • Connect it to the closest not j
  • C(i,j)
  • remaining notes C'


Step 2
  • Choose a member from C' closest to C call it n
  • C(i,j,n)
  • C'= C'-n


Step 3
  • repeat


Constantly check the thing as a whole!

In MST what do the following represent?
  • V
  • G
  • E
  • G'   

  • V Vertices of a graph
  • G Items we wish to connect
  • E items that can be directly linked
  • G' Spanning tree since removing one vertex does not reduce connectivity   
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How can you prevent cycling in MST?

  • Sum Xij = n-1
  • sum xij = |V'| - 1

What is the difference between MST and TSP?

In TSP you visit every location only once.

In TSP what is
  • tour
  • symmetric
  • Assymetric

tour
any route visiting each city once;

symmetric
dij = dji

Assymetric
dij is not dji

In TSP what are the subset elemination constraints? [2]

Sum xij =< |S| - 1

3 =< |S| =< |V| -3

What is ocnsidered to be a tree?

Connected acyclic graph with no cycles

In graph C.O.P. (Combinatorial Optimization Problem) graph theory what are theorems?

Theorem 1
A graph is a tree when there is exactly one path between each pair of vertices;

Theorem 2
A tree with n vertices has n-1 edges;

Theorem 3
Any connected graph with n vertices and n-1 edges is a tree;

Theorem 4
A graph is minimally connected when removal of any edge disconnects the graph;

Theorem 5
A graph is a tree only when it is minimally connected;

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