Forward feature selection for support vector machines

1. A method comprising:

defining an iteration counter to a predetermined value;

training, using a processor of a computer system, a Support Vector Machine (SVM) on a subset of features (d′) of a feature set having (d) features of a plurality of training instances to obtain a weight per instance ({right arrow over (α)}′);

approximating a quality for the d features of the feature set using the weight per instance;

ranking the d features of the feature set based on the approximated quality;

selecting a subset (q) of the features of the feature set based on the ranked approximated quality; and

iterating training the SVM, approximating the quality, ranking the d features, and selecting the q subset until the q subset is less than a selected threshold.

2. The method of claim 1 , further comprising incrementing the iteration counter.

3. The method of claim 2 , further comprising iterating training the SVM, approximating the quality, ranking the d features, and selecting the q subset if the iteration counter is less than a second predetermined value.

4. The method of claim 1 , wherein ranking the d features includes comparing rank values each based at least in part on each of the approximated quality to a threshold.

5. The method of claim 4 , wherein selecting the q subset includes selecting features having a corresponding approximated quality greater than the threshold.

6. The method of claim 5 , further comprising approximating the feature quality by an approximate weighted correlation between instance labels and values for the features.

7. The method of claim 1 , wherein d′ is substantially less than d and is a random subset of d.

8. The method of claim 7 , wherein d′ is less than d by at least a factor of one hundred.

9. The method of claim 1 , wherein each of the plurality of training instances corresponds to an image.

10. The method of claim 1 , wherein the SVM comprises a linear SVM.

11. The method of claim 1 , wherein the weight per instance comprises a vector (α′) of a length N corresponding to the plurality of training instances.

12. An article comprising a non-transitory machine-accessible medium including instructions that when executed cause a system to:

define an iteration counter to a predetermined value;

train a Support Vector Machine (SVM) according to a forward feature selection algorithm in which only a random subset of features (d′) of a feature set (d) of a plurality of training instances are used to obtain a weight per instance (α′);

approximate a quality for the d features of the feature set using the weight per instance;

rank the d features of the feature set based on the approximated quality, and select a subset (q) of the features of the feature set based on the ranked approximated quality;

classify unlabeled data using the trained SVM; and

determine whether the q subset is less than a first threshold, and if so conclude the SVM training, and otherwise iterate training the SVM, approximating the quality, ranking the remaining q features from the previous iteration, and selecting the q subset until the q subset is less than the first threshold.

13. The article of claim 12 , further comprising instructions to compare rank values each based at least in part on the approximated quality of each of the features to a second threshold.

14. The article of claim 13 , further comprising instructions to select the q subset by selecting features having a corresponding approximated quality greater than the second threshold.

15. A system comprising:

a processor to perform instructions; and

a memory coupled to the processor to store instructions that enable the processor to define an iteration counter to a predetermined value, train a Support Vector Machine (SVM) on a subset of features (d′) of a feature set having (d) features of a plurality of training instances to obtain a weight per instance, approximate a quality for each of the d features of the feature set using the weight per instance, rank the d features of the feature set based on the approximated quality, select a subset (q) of the features of the feature set based on the ranked approximated quality, determine whether the q subset is less than a first threshold, and if so conclude the SVM training, and iterate training the SVM, approximating the quality, ranking the remaining q features from the previous iteration, and selecting the q subset until the q subset is less than the first threshold if the q subset is greater than the first threshold.

16. The system of claim 15 , further comprising instructions to compare rank values each based at least in part on each of the approximated quality to a second threshold.

17. The system of claim 16 , further comprising instructions to select features having a corresponding approximated quality greater than the second threshold.

18. The system of claim 15 , further comprising instructions to approximate the quality by an approximate weighted correlation between a label per instance and values for the features.

19. The system of claim 15 , wherein the SVM is a forward feature selection SVM.

20. The system of claim 15 , wherein the d′ subset is a random subset.