# Multi-target tracking "assignDet​ectionsToT​racks" function has unexpected results?

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cui on 2 Jul 2020
Commented: cui on 12 Sep 2020
When I use the "assignDetectionsToTracks" function, the 5th (row) tracking is associated with the (1)th col detection, and the threshold(costOfNonAssignment=1) I set is 1, and there should be no correlation. Why?
cost = [2.62407,1.93346,4.28524,0.0126375;
1.34658,3.33612,0.769382,3.78107;
2.04141,0.012594,3.98619,1.92012;
3.35982,2.04044,5.14111,1.01901;
1.59666,3.05409,2.13898,2.69844;
4.54989,6.35886,3.17712,6.65899];
costOfNonAssignment = 1;
[assignment,unassignedTracks,unassignedDetections] = ...
assignDetectionsToTracks(cost,costOfNonAssignment)
assignment =
4×2 uint32 matrix
5 1
3 2
2 3
1 4
unassignedTracks =
2×1 uint32 column vector
4
6
unassignedDetections =
0×1 empty uint32 column vector
As can be seen from the result assignment, the fifth track is associated with the first detection data, and the cost between them is 1.59666, and the threshold I set is 1, the cost is greater than the threshold, why the fifth track Related to the first test? Shouldn’t it belong to unassignedTracks?

Elad Kivelevitch on 8 Sep 2020
The fifth row / first column is associated because if these were not associated you would incure a cost of unassignment for both row and column, meaning 1+1 = 2. 2 is greater than 1.59666 so the assignment is favored instead of unasignment.
cui on 12 Sep 2020
Thank you for your detailed explanation, 1+1=2, and the two 1s represent "unassignedTrackCost" and "unassignedDetectionCost" respectively. I can explain it by specifying the two costs in detail in the following way.
unassignedTrackCost = 0.5;
unassignedDetectionCost = 1;
[assignment,unassignedTracks,unassignedDetections] = ...
assignDetectionsToTracks(cost,unassignedTrackCost,unassignedDetectionCost)

R2020a

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