
I'm fascinated by the fact that we can learn unobserved structures of the data in a principled manner.
I've been focusing on spectral learning of latentvariable models.
Publications

Karl Stratos, Dokyum Kim, Michael Collins, and Daniel Hsu.
A Spectral Algorithm for Learning ClassBased ngram Models of Natural Language. [pdf]
In Proceedings of UAI (2014).
 Here's a longer version that has an appendix on sample complexity.
 Here's code cca I used for deriving word embeddings as described in this paper.
 Here's code greedo for greedy agglomerative clustering of word vectors.

Shay B. Cohen, Karl Stratos, Michael Collins, Dean P. Foster and Lyle Ungar.
Spectral Learning of LatentVariable PCFGs: Algorithms and Sample Complexity [pdf].
In JMLR (2014).

Karl Stratos, Alexander M. Rush, Shay B. Cohen, and Michael Collins.
Spectral Learning of Refinement HMMs [pdf][slides].
In Proceedings of CoNLL (2013).

Shay B. Cohen, Karl Stratos, Michael Collins, Dean Foster and Lyle Ungar.
Experiments with Spectral Learning of LatentVariable PCFGs [pdf].
In Proceedings of NAACL (2013).

Shay B. Cohen, Karl Stratos, Michael Collins, Dean Foster and Lyle Ungar.
Spectral Learning of LatentVariable PCFGs [pdf][slides].
In Proceedings of ACL (2012).

Alexander C. Berg, Tamara L. Berg, Hal Daum III,
Jesse Dodge, Amit Goyal, Xufeng Han, Alyssa Mensch,
Margaret Mitchell, Aneesh Sood, Karl Stratos, Kota Yamaguchi
Understanding and Predicting Importance in Images
[pdf].
In Proceedings of CVPR (2012).

Karl Stratos, Lenhart K. Schubert, and Jonathan Gordon.
Episodic Logic: Natural Logic + Reasoning [pdf].
In Proceedings of KEOD (2011).

Lenhart Schubert, Jonathan Gordon, Karl Stratos, and Adina Rubinoff.
Towards Adequate Knowledge and Natural Inference [pdf].
In Proceedings of AAAI Fall Symposium on Advances in Cognitive Systems (2011).
Activities
2013 Summer: I had the privilege of interning with Sham Kakade and T. J. Hazen
at Microsoft Research New England.
2013 Summer: We gave a tutorial on spectral methods in NLP at NAACL 2013! Video [Part 1] [Part 2]
2011 Summer: I participated in the
summer workshop at JHU CLSP
as part of the "vision" team. I worked mainly on analyzing and modeling what people choose to describe in an image.
20102011: At URCS, I was part of the
KNEXT project, a joint endeavor of
Len Schubert,
Jonathan Gordon, and
Benjamin Van Durme (among others) to extract
commonsense knowledge out of textual resources.
Informal Writings
These are just for fun.

Notes on the framework of Ando and Zhang (2005) [pdf].

Max margin training ("support vector machines") [pdf].

Shiftreduce dependency parsing [pdf].

Approximate CCA [pdf].

A Hitchhiker's Guide to PCA and CCA [pdf].

The Lorentz transformation [pdf].

A formulation of the EM algorithm for PCFGs [pdf].

A formulation of the EM algorithm for HMMs [pdf].

