ubiquitous computing aims to create intelligent environments saturating with computing and communication capabilities such that people access ubiquitous applications without knowing underlying technologies .this intelligence is mainly achieved by context - awareness , which assists ubiquitous applications in adapting to changeable contexts  .contexts refer to pieces of information that captures the features of ubiquitous computing environments  .the checking of context consistency is fundamental to ubiquitous computing .for example , a rfid - based system may acquire two different locations of a user at the same time  .this kind of context consistency must be checked .however , contexts are often noisy owing to the unreliable connectivity and resource constraints  .moreover , contexts frequently keep evolving with user mobility and situations  .therefore , the detection of context consistency is a non - trivial problem .a variety of schemes for checking context consistency have been proposed . in  ,context consistency was specified by ontology assertions such that it could be checked by hidden rules and axioms from ontology . in , context consistency was modeled by tuples and resolved by _ drop - all _ and _ drop - best _ policies without delineating the checking context consistency . in  , a tree - based checking scheme based on the first - order logicwas reported that checked context consistency by refining consistency trees using partial context constraints . however , most existing schemes are seriously limited by two problems .one is that they are centralized , which incurs their unscalability in large - scale ubiquitous environments with a huge number of nodes .the other is that they fall short when counting in temporal relations among context events , since they implicitly assume that contexts being checked belong to the same snapshot .but this assumption can not be always held in ubiquitous computing environments that are characterized by asynchronous cooperation and schedule .  to removethe above assumption , ceda  was proposed .it mapped the context consistency checking into context event detection , and checked concurrent context events based on the _ happened - before _however , ceda suffers from three drawbacks , as shown in our previous work  .firstly , it checked event detection in a centralized manner , incurring its less effectiveness in large - scale ubiquitous applications .secondly , it introduced false negative because _ happened - before_ relation can not accurately capture all event relations .finally , ceda suffered heavy time and space complexity , which led to its poor performance .  to this end, we propose in this paper seca snapshot - based event detection for context consistency checking , which is built on top of time snapshots and logical clocks .seca detects context consistency in a distributed manner , which enables the checking nodes not to be blocked or become system bottle - necks .it adopts logical clocks instead of vector clocks to evaluate event relations . to be scalable , seca customizes logical clocks by holding the value part .thus , it detects event relations that ceda can and can not . theoretical analysis and extensive experimental results show that seca achieves higher detection accuracy than ceda in a more scalable manner .the main contributions of this paper are three - fold .* first , seca removes the limitation held by ceda that central - based checking systems are easily to get heavy computing load .in contrast , seca achieves its function in a fully - distributed manner , which is highly desirable in large - scale mobile ubiquitous computing . *second , seca is capable of detecting false negative scenarios where ceda fails by introducing the snapshot timestamp . *finally , seca respectively reduces ceda s complexity of time and space for handling an event from to and from to , where is the number of nodes in ubiquitous network .the remaining of this paper is structured as follows .section [ sec : sca ] presents the design of seca , followed by theoretical analysis .section [ sec : experiment ] reports our extensive experimental results .section [ sec : conclusion ] concludes the paper with a summary and the future work .generally , ubiquitous computing environments are modeled as a loosely - coupled distributed system , where physical entities ( e.g. , objects and users ) sense environments , and ubiquitous infrastructures handle sensed data and deliver services to ubiquitous applications . in the following , we start with introducing our system formulation .suppose , , , be asynchronous processes in a ubiquitous computing environment , be an event set in process , and and be the start and end of an event , respectively . thus the event is modeled as an interval .note that processes communicate with each other only by means of message - passing , and the communication delay is finite but unbounded .  in this subsection, we first introduce the concept of snapshot timestamp and its update policy , and then reshape the _ happened - before _relation with the snapshot timestamp .  * snapshot timestamp . *it refers to an implementation of the logical clock , where all nodes maintain a logical clock . in the system of snapshot clocks ,the time domain is denoted as a set of and non - negative integer clocks .each process maintains a snapshot clock |k=1, ... ,n\} ] is the local logical timestamp and describes the logical time progress at .the process updates its snapshot clock by rules 1 and 2 .  1 .  before sending a message , the process updates its local clock by = s_i[k-1 ] + d ( d > 0),\ ] ] where the default value of is 1 .then , the process piggybacks a message with its snapshot clock to the remaining nodes in the same environment .when receiving a message )$ ] from the process , the process gets the snapshot timestamp at a point as : = max(s_i[k ] , s_j[send ] ) , ( 1 \leq k \leq n)\ ] ]  figure [ fig : snapshot - clock ] illustrates the update policies of our snapshot clock algorithm , where events are represented by the start and end of intervals i.e. , and .when the process would like to send a message , it will automatically increment the value of its snapshot clock , and then delivers the message to the processes and .+  evidently , by comparing timestamps ( i.e. , an array of elements ) , the snapshot clock keeps its property of isomorphism .the relations between timestamp intervals include two ordering relations represented as and , and one concurrent relation denoted as .  [ property : isomorphism ] given two timestamp intervals and ( a timestamp interval may contain a number of logically continuous timestamps ) , the isomorphism of the snapshot clock is given as : \leq i_q[i ' ] \nonumber \\i_p < i_q & \leftrightarrow & i_p \leq i_q \textbf{\ , and \ , } \exists i , i ' \ , i_p[i ] < i_q[i ' ] \nonumber \\     i_p \parallel i_q & \leftrightarrow & \textbf{not \,}(i_p< i_q ) \textbf{\ , and not \ , } ( i_q <     i_p ) \nonumber   \end{aligned}\ ] ]  * snapshot - based _ happened - before _relation .* let denotes the _ happened - before _relation , the snapshot timestamps based events in a distributed system satisfy theorem [ property : snaps-2 ] .[ property : snaps-2 ] given two events and with respective timestamp intervals and , then :   according to the update policies of snapshot clocks , the _ happened - before _relation is held .thus , an isomorphism exists between the partially ordered events produced by a distributed computation and their timestamps .this is a powerful and interesting property of snapshot clocks .note that the _ happened - before _relation between these two events is stated as .  in order to easily detect concurrent events, we propose an event concurrence detection mechanism shown as theorem [ pro : snap - clock ] .[ pro : snap - clock ] given two events and in processes and .assume the event sends a message to the event with its timestamp , then :   (   )   and , where   . ]there is a message from the event to the event .according to the update policy of snapshot clock , the value of is not less than .meanwhile , the message is handled by the event , indicating that the value of must be less than .   in this paper, we propose a seca scheme snapshot - based event detection for checking asynchronous context consistency in ubiquitous computing .seca is built on top of the snapshot timestamps , and enables all nodes to detect concurrent context consistency events without central control or a centralized hierarchy . in seca ,the basis of context consistency detection is theorem [ pro : snap - clock ] and _ happened - before _figure [ fig : concurrent - event ] illustrates the fact that the events and are concurrent , which is checked by theorem [ pro : snap - clock ] .the pseudo - code of seca scheme is given as algorithm [ algorithm : process ] , consisting of three parts : event processing , message processing , and context consistency checking .the event processing refers to a process that updates its snapshot clock when an event occurs within its life span . to be specific, the process updates its snapshot clock , the event queue , as well as interval queue by broadcast ( e.g. , seca offers a primitive ) . when events communicate with messages , the processes where the events happen meet two types of message processing sending and receiving .the sender is in charge of updating the event queue and interval queue ( see steps 11 - 14 ) . correspondingly , the receiving process modifies its snapshot clock by picking the maximal timestamp value between the snapshot timestamps of the sender and receiver processes ( see steps 15 - 19 ) .note that the actions of senders and receivers are incorporated together in the pseudo - code .the third part refers to the context consistency detection . since elements in implicitly satisfy theorem [ pro : snap - clock ] , we output the event pairs simply by a validation check .thus far we have presented the design of seca .however , does seca scheme solve false negative caused in ceda scheme ?can seca scheme detect context consistency accurately in ubiquitous computing environments ?we investigate these issues by theoretical analysis in this section .specially , we will study the false negative , complexity and implementation manner of the proposed scheme .moreover , in the following section [ sec : experiment ] , we further evaluate seca by extensive experiments .given intervals , , , , ceda checks concurrent context consistency events by eq .[ eq : ceda ] , which is built on top of _ happened - before _the case of interval overlaps which is characterized by concurrent events shown as fig .[ fig : ceda - detection ] .however , for some concurrent events whose intervals are overlapped , the ceda scheme fails to detect them , which is notorious for * false negative * phenomena .this is because eq .[ eq : ceda ] can not detect these overlapping intervals although they are mutual across .   +  figure [ fig : ceda - false - negative ] illustrates three false negative scenarios where ceda scheme fails to check context consistency correctly . in figs .[ fig : false - negative - a ] , [ fig : false - negative - c ] and [ fig : false - negative - c ] , two events in two respective processes satisfy , , and , respectively .these two events concurrently take place , but eq . [ eq : ceda ] are blind of them . on the contrary, seca is capable of successfully identifying these concurrent context events . as for figs .[ fig : false - negative - a ] and [ fig : false - negative - b ] , seca compares the message timestamp of senders with the and of the receivers and then locates the concurrency . note that concurrency in fig .[ fig : false - negative - c ] is challenging to detect .this kind of concurrency is mainly caused by message delay .owing to the space limitation , we only report the experimental results about how message delay affects the seca performance , and omit the part of theoretical analysis .   taking a panoramic view of the seca scheme , it is easy to find that seca does not rely on central control to check context consistency .all processes involved in a ubiquitous system are equal and check context consistency by snapshot clocks .every process requires space complexity to maintain snapshot timestamps , and time complexity for every context consistency event detection . considering that many ubiquitous devices are with limited computing and communication capabilities , seca is highly desirable with respect to efficiency and scalability in large - scale mobile ubiquitous environments .  to further evaluate the time and space complexity of the proposed scheme, we have implemented the detection schemes by physical clocks , vector clocks and snapshot clocks , labeled as pca , ceda and sca schemes , correspondingly .table [ tbl : theorectical - comparison ] compares the pca , ceda and sca in terms of clock synchronization , handling the occurrence of an event , detecting overlapped intervals and concurrent events , and false negative . by comparison ,sca significantly alleviates the time and space complexity concerning event processing and context consistency checking .meanwhile , sca also cuts off a half possibility of false negative generated in ceda scheme ..comparison of pca , ceda and sca schemes with respect to checking context consistency events [ cols="<,<,<,<",options="header " , ]   in general , seca scheme can be achieved in a distributed manner , the same as that of _ happened - before _relation implementation in distributed systems .this kind of implementation is appropriate to pcs and supercomputers that are equipped with powerful communication and computation capabilities . with respect to the hand - held and embedded devices , e.g. , sensors , rfid , and mobile phones, the proposed scheme can be reached by agents , e.g. , mobile agents for rfid and mobile phones  .we conduct extensive experiments in this section to further evaluate whether seca is appropriate to context - aware applications in asynchronous ubiquitous computing environments .in particular , this section will evaluate how the detection accuracy of seca is , and whether seca outperforms ceda regarding detection accuracy and computation cost .a smart building scenario is simulated where users move around .the duration of users stay in an office follows the exponential distribution . in view of that user locationis regarded as the most important type of contexts in asynchronous ubiquitous computing environments  , the user location is our focus .the holistic study environment is equipped with rfid devices and every user carries a rfid tag such that the location context is collected timely .the rfid data concerning user location is generated with controlled error rates of 10% , 20% , 30% , 40% and 50% by leveraging on the mechanisms provided in the existing literature  .a constraint is implanted into the location context that * _ a user can not have two difference locations at the same time_*.   a series of experiments is designed to check the detection accuracy of seca and whether it performs better than ceda .given that the experiments shed light on detecting concurrent events of user locations , we limit the number of nodes attending for the same contexts from 2 to 20 .every node runs two detection process instances .every event has a random life span from 20 milliseconds to 50 milliseconds and every message suffers a random delay between 0.25 to 8 seconds .all experimental results are gained by pc equipped with windows enterprise 7 ( 32-bit ) , cpu 1.67ghz , and ram 2 gb . the following experiments share the same settings without explicit declaration .figure [ fig : performance](a ) illustrates the performance results with tuning the number of nodes from 2 to 20 . both ceda and seca schemes achieve a high level of detection accuracy of context consistency events , showing a slightly downward trend .this indicates that vector clocks and _ happened - before _relation is efficient for detecting concurrent context consistency events .meanwhile , seca scheme acquires a higher level of accuracy than ceda .this is because seca correctly solves part of cases where ceda gets false negative errors .several experiments are conducted to investigate how the message delay affects the concurrent event detection of the proposed scheme .  as shown in fig .[ fig : performance](b ) , detection accuracy of both seca and ceda schemes reduce their accuracy as the increase of message delay . in all experiments , seca achieves a higher level of accuracy than ceda owing to its snapshot - based timestamp checking mechanism .especially , when the logarithm of the message delay is between -2 and 3 , seca gets a better detection accuracy with less communication overheads .taking into account the scale of ubiquitous network , we hereby set the value of message delay as 0.25 to 8 milliseconds .in this paper , we have studied concurrent event detection for checking context consistency in asynchronous ubiquitous environments .we have proposed the snapshot timestamp and based on it we have put forward the seca scheme , which reduces the time complexity of ceda from to , and the space complexity for handling an event from to , where is the scale of ubiquitous network .extensive experimental results show that seca is desirable in context - aware applications and outperforms ceda regarding concurrent event detection accuracy , and robustness on message delay and event duration .currently , seca scheme could be further improved in the following perspectives .firstly , we need to investigate how seca performs in large - scale ubiquitous computing environments with over ten thousands of participants . secondly , we will study whether and how seca copes with the dynamic changes of processes involved in the concurrent event detection .finally , we plan to evaluate seca in various scenarios with more types of contexts and consistency constraints .this work is supported by the national natural science foundation of china ( grant nos .61103185 , 61100178 , 61003247 and 61073118 ) , the start - up foundation of nanjing normal university ( grant no .2011119xgq0072 ) , and natural science foundation of the higher education institutions of jiangsu province , china ( grant no .11kjb520009 ) .this work is also supported by major program of national natural science foundation of jiangsu province ( grant no .bk211005 ) .this research was also partially supported by the national research foundation of korea ( nrf ) grant funded by the korea government ( mest ) ( grant no . 2011 - 0009454 ) .d. zhang , h. huang , c .- f .lai , x. liang , q. zou , and m. guo , `` survey on context - awareness in ubiquitous media , '' _ multimedia tools and applications _ , pp . 133 , 2012 , 10.1007/s11042 - 011 - 0940 - 9 .[ online ] .available : http://dx.doi.org/10.1007/s11042-011-0940-9  y. huang , x. ma , j. cao , x. tao , and j. lu , `` concurrent event detection for asynchronous consistency checking of pervasive context , '' _ proc . of the ieee int .conf . on perv. comput . and commu ._ , pp . 19 , 2009 .d. zhang , m. guo , j. zhou , d. kang , and j. cao , `` context reasoning using extended evidence theory in pervasive computing environments , '' _ future generation comp ._ , vol . 26 , no . 2 , pp .207216 , 2010 .d. zhang , h. guan , j. zhou , f. tang , and m. guo , `` ishadow : yet another pervasive computing environment , '' in _ ieee international symposium on parallel and distributed processing with applications_.1em plus 0.5em minus 0.4emsydney , nsw , australia : ieee , 2008 , pp . 261268 .x. wang , d. zhang , t. gu , and h. pung , `` ontology based context modeling and reasoning using owl , '' in _ _ proc . of the 2nd ieee annual conf .comput . and commu .work.__1em plus 0.5em minus 0.4emieee , 2004 , pp .y. bu , s. chen , j. li , x. tao , and j. lu , `` context consistency management using ontology based model , '' in _ current trends in database technology edbt workshops _4254.1em plus 0.5em minus 0.4em springer , 2006 , pp. 741755 .y. bu , t. gu , x. tao , j. li , s. chen , and j. lu , `` managing quality of context in pervasive computing , '' in __ proc . of the 6th .int . conf . on quality softw.__1em plus0.5em minus 0.4emieee , oct . 2006 , pp. 193200 .d. zhang , m. chen , h. huang , and m. guo , `` decentralized checking of context inconsistency in pervasive computing environments , '' _ the journal of supercomputing _ , pp . 118 , 2012 , 10.1007/s11227 - 011 - 0661-x .[ online ] .available : http://dx.doi.org/10.1007/s11227-011-0661-x

Abstract: context - consistency checking is challenging in the dynamic and uncertain ubiquitous computing environments . this is because contexts are often noisy owing to unreliable sensing data streams , inaccurate data measurement , fragile connectivity and resource constraints . one of the state - of - the - art efforts is ceda , which concurrently detects context consistency by exploring the _ happened - before _ relation among events . however , ceda is seriously limited by several side effects centralized detection manner that easily gets down the checker process , heavy computing complexity and false negative .  in this paper , we propose seca : snapshot - based event detection for checking asynchronous context consistency in ubiquitous computing . seca introduces snapshot - based timestamp to check event relations , which can detect scenarios where ceda fails . moreover , it simplifies the logical clock instead of adopting the vector clock , and thus significantly reduces both time and space complexity . empirical studies show that seca outperforms ceda in terms of detection accuracy , scalability , and computing complexity .


ranking from pairwise comparisons or _ preferences _ is an ubiquitous problem in machine learning , statistics and theoretical computer science . in theso - called _ non - active _ setting , one is given comparison results of pairs pre - selected from among all pairs of items where each pair is compared at least times . particularly , the learner does not get to choose which pairs are to be compared .the goal is then to estimate a suitable ordering of the items , using the observed comparison results , that conforms to the true ordering , assuming one exists , up to the desired error in a suitably defined error measure .  in practical ranking applications, we often have side information associated with the items that need to be ranked such a scenario is referred to as the _ inductive _ setting .an advantage in this inductive learning setting is that , in addition to ranking a given set of items , one is also able to rank new unseen items that may introduced after parameter learning .motivated by these factors , we wish to leverage the available side information to compute an ordering more efficiently than existing techniques .this is relevant in many practical applications ; for instance , in addition to using a minimal amount of customer preference data , ( a ) using food characteristics like nutrition , preparation method , etc could help in finding the top - rated dishes of a restaurant , ( b ) using car features like engine type , body type , etc could help elicit useful trends for automotive industry .[ [ our - contributions ] ] our contributions : + + + + + + + + + + + + + + + + + + +  to the best of our knowledge , our work is the first to derive a provable and efficient method for ranking in the non - active inductive setting . our novelty and technical contributions can be summarized along the following axes :  1 ._ model : _ we generalize existing models so that we can incorporate ( a ) features , and ( b ) feature correlations associated with the items to be ranked . we show that our model subsumes many existing and popular ranking models ._ algorithm : _ our algorithm uses two key subroutines namely , ( a ) noisy inductive matrix completion , and ( b ) approximate pairwise ranking algorithm  .guarantee : _ we derive the guarantee that our algorithm obtains , with high probability , an -accurate recovery using independent pairwise comparisons chosen uniformly at random .experiments : _ we substantiate our theoretical results by demonstrating sample complexity gains on both synthetic and real - world experiments .we would like to emphasize upfront that it is the sole focus of this paper to study the practically motivated regime of in detail .furthermore , we note that our sample complexity results do not violate the standard lower bounds for comparison - based sorting algorithms since we develop an algorithm that effectively ranks in the _ feature space _ rather than the _ item space_.   we now give a brief overview of relevant work in ranking models followed by a brief background regarding tools from inductive matrix completion theory which will be crucial in proving our sample complexity bounds .[ [ ranking - models ] ] ranking models : + + + + + + + + + + + + + + + +  in the simplest terms , the ranking problem involves estimating the _ best _ ordering items according to some observed preferences .a early thread of ranking literature has its beginnings in economics involving choice models  ; other related works in social choice theory include and . a certain deterministic version of the ranking problem is also studied as the _ sorting _ problem which is central in theoretical computer science .  1.  _ random utility ( ru ) models : _ starting with the seminal work of , the bradley - terry - luce ( btl ) model has become a landmark model for ranking . in the vanilla version of this model ,the probability that item beats item is given by where is the parameter vector to be estimated from data ; the entry in denotes the _ score _ associated with item .thurstone  model is also a well - known statistical model ; here , where is the standard normal cumulative distribution function ( cdf ) and is the score vector .these classic models fall under the so - called _ random utility _( ru ) models  ._ item feature ( if ) models : _ extending the btl model , statistical models that utilize side information are presented in .recently , presented the blade - chest ranking model which studied the stochastic intransitive setting .their algorithm involves regularized maximum likelihood estimation for which tight sample complexity properties are not known . despite the above works , to the best of our knowledge , there are no known models utilizing feature information while have provable sample - efficient algorithms for estimation and ranking .low rank ( lr ) models : _ recently ,  unifying classic models such as btl and thurstone models defined a generic class of preference matrices which have low rank under transformations involving suitable _ link functions_. upon such a transformation ,connections of the ranking problem to matrix completion theory become clear .subsequently , they use well - known matrix completion results to derive sample complexity guarantees for ranking .however , their model does not utilize side information that may be available .this list is by no means exhaustive ; while there exist several other ranking methods ( eg , ranking - svm ) , there are no known sample complexity guarantees associated with these .[ [ inductive - matrix - completion ] ] inductive matrix completion : + + + + + + + + + + + + + + + + + + + + + + + + + + + + +  the matrix completion task  is to fill - in the missing entries of a partially observed matrix , which is possible efficiently under a low - rank assumption on the underlying matrix .oftentimes , side information may be available which further makes this task potentially easier .this is the _ inductive matrix completion _( imc ) problem which is formally defined as the optimization problem , where and are known feature matrices , is a rank- unknown latent parameter matrix , \times [ n] ] ; concatenating these , we obtain the feature matrix \in { \mathbb{r}}^{d \times n} ] which is a strictly increasing bijective function is a valid link function . for example , could be the logit function , which is the inverse of the sigmoid function , defined as , for  ] denote the set of all pairwise preference matrices over items .let the set of stochastic - transitive matrices be and the set of stochastic - intransitive matrices be .let be the set of preference matrices associated with unary random utility models ( which are described in the next section ) .let for some .let .define the set of preference matrices having rank- under the link function as .next , define the set of preference matrices having rank- under the link function with the associated feature matrix as where is an unknown rank- latent matrix ( which is a function of the parameters of the ranking model ) and \in { \mathbb{r}}^{d \times n} ] ,  ] .let be the set of pairs of items compared such that the number of pairs compared is where is chosen uniformly at random from among all possible subsets of item pairs of size .let each pair in be compared independently times where .then , with probability atleast , for any , algorithm [ alg : ipr ] returns an estimated permutation such that .  the key take - away message in theorem [ thm : main ] is the reduction in sample complexity possible due to efficient utilization of features and feature correlations , associated with the items to be ranked , by algorithm [ alg : ipr ] .for instance , when , which is often the case in practice , we reduce the required total number of comparisons to be made to . thus , we achieve a very significant gain since the total number of comparisons is poly - logarithmic as opposed to quadratic in the number of items .this is especially crucial in large - scale machine learning applications .another point to be noted from theorem [ thm : main ] is that , under the uniform sampling assumption , when features associated with items are known , it is more important that we compare sufficient ( precisely , ) number of different pairs rather than high number of comparisons per pair .furthermore , he total number of comparisons needed in theorem [ thm : main ] is given by the product which is .we now present the proof of theorem [ thm : main ] .we shall prove the theorem under the bernoulli sampling model ( where each entry of an matrix is observed independently with probability ) rather than the uniform sampling model ( wherein is chosen uniformly at random from among all possible subsets of item pairs of size ) ; the equivalence between the two is well - known ( see , for instance , section 7.1 of ) . for \times [ n] ] using the preferences of all the customers and consider this to be ground truth preference matrix . an interesting observation was that , over five runs of the algorithms , ipr gets two out of the top four sushi dishes right most of the times namely , ` amaebi ' and ` ikura ' ; on the other hand , lrpr does not succeed in recovering these always .car : _ the task in this dataset  is find an order of preference among ten cars .this data was collected by surveying customers regarding there preferences among pairs of cars drawn from the set of ten cars .each car has four features including engine , transmission and so on .we construct the ground truth preference matrix ^{10 \times 10}$ ] by aggregating the pairwise preferences of all the customers .an interesting trend we found was that customers generally preferred sedans over suvs and non - hybrid vehicles over hybrid vehicles .in this paper , we have proposed and characterized the flr model together with the guaranteed ipr algorithm that utilizes available side information of the items to be ranked to provably reduce the sample complexity for ranking from to possibly as low as .a future research direction is to see if mixture models for ranking such as the recently proposed topic modeling approach  could fit into our framework while admitting sample - efficient estimation algorithms .abbasnejad , e. ; sanner , s. ; bonilla , e. v. ; poupart , p. ; et al .. learning community - based preferences via dirichlet process mixtures of gaussian processes . in _ijcai_.  bradley , r. a. , and terry , m. e. 1952 .rank analysis of incomplete block designs : i. the method of paired comparisons .39(3/4):324345 .cands , e. j. , and recht , b. 2009 .exact matrix completion via convex optimization .9(6):717772 .cands , e. j. ; li , x. ; ma , y. ; and wright , j. 2011 .robust principal component analysis ?58(3):11 .caragiannis , i. ; procaccia , a. d. ; and shah , n. 2013 .when do noisy votes reveal the truth ? in _ proceedings of the fourteenth acm conference on electronic commerce _ , 143160 .cattelan , m. 2012 .models for paired comparison data : a review with emphasis on dependent data. 412433 .chen , s. , and joachims , t. 2016 .modeling intransitivity in matchup and comparison data . in _ proceedings of the ninth acm international conference on web search and data mining _ , 227236 .chiang , k .- y . ; hsieh , c .- j . ; and dhillon , i. s. 2015 .matrix completion with noisy side information . in _ advances in neural information processing systems _ , 34473455 .copeland , a. h. 1951 . a reasonable social welfare function . in _mimeographed notes from a seminar on applications of mathematics to the social sciences , university of michigan_.  coppersmith , d. ; fleischer , l. ; and rudra , a. 2006 .ordering by weighted number of wins gives a good ranking for weighted tournaments . in _ proceedings of the seventeenth annual acm - siam symposium on discrete algorithm _, 776782 .society for industrial and applied mathematics .  ding , w. ; ishwar , p. ; and saligrama , v. 2015 .a topic modeling approach to ranking . in _aistats_.  jain , p. , and dhillon , i. s. 2013 .provable inductive matrix completion . .ji , s. , and ye , j. 2009 .an accelerated gradient method for trace norm minimization . in _ proceedings of the 26th annual international conference on machine learning _ , 457464 .joachims , t. 2002 . optimizing search engines using clickthrough data . in _ proceedings of the eighth acm sigkdd international conference on knowledge discovery and data mining _ , 133142 .kamishima , t. , and akaho , s. 2009 .efficient clustering for orders . in _ mining complex data_. springer .261279 .lu , t. , and boutilier , c. 2011 . learning mallows models with pairwise preferences . in _ proceedings of the 28th international conference on machine learning ( icml-11 )_ , 145152 .luce , r. d. 1959 . .john wiley and sons .marschak , j. , et al . 1959 .binary choice constraints on random utility indicators . technical report ,cowles foundation for research in economics , yale university .rajkumar , a. , and agarwal , s. 2016 .when can we rank well from comparisons of non - actively chosen pairs ? in _29th annual conference on learning theory _, 13761401 .thurstone , l. l. 1927 . a law of comparative judgment .34(4):273 .xu , m. ; jin , r. ; and zhou , z .- h . 2013 .speedup matrix completion with side information : application to multi - label learning . in _ advances in neural information processing systems _ , 23012309 .we prove this by showing that every is in but not the other way around . by the definition of a preference matrix corresponding to the lr model , if , then .similarly , for the flr model , if , then and ; in other words , . now setting , we have . on the other hand ,if , we have .let be the unary score vector in ru models .the result then follows by setting the energy function of item with respect to item in the flr model to be the unary score corresponding to item in the ru model , ie , by simply setting and which leads to .this is immediate by setting . for concreteness , we choose to be the logit link function . setting in equation 1, we obtain observe that . writing this in matrix notation , .note that is a rank- skew - symmetric matrix .let .now , note that is also a rank- skew - symmetric matrix .thus , since .in addition , note that the flr model accounts for feature correlations when .for any support , define the following event : by hoeffding s bound , whenever .let be the lipschitz constant of and set .using the inequality that , we have

Abstract: we study the problem of ranking a set of items from non - actively chosen pairwise preferences where each item has feature information with it . we propose and characterize a very broad class of preference matrices giving rise to the _ feature low rank _ ( flr ) model , which subsumes several models ranging from the classic bradley terry  luce ( btl )  and thurstone  models to the recently proposed blade - chest  and generic low - rank preference  models . we use the technique of matrix completion in the presence of side information to develop the inductive pairwise ranking ( ipr ) algorithm that provably learns a good ranking under the flr model , in a sample - efficient manner . in practice , through systematic synthetic simulations , we confirm our theoretical findings regarding improvements in the sample complexity due to the use of feature information . moreover , on popular real - world preference learning datasets , with as less as 10% sampling of the pairwise comparisons , our method recovers a good ranking .


as beings bound to a small planet orbiting an unexceptional star in the outskirts of a galaxy that is one among trillions , how can we hope to understand the universe ?astronomers approach this problem by drawing on two key ideas .the first is the cosmological principle , an infinite extrapolation of the copernican discovery that displaced the earth from its special location at the center of everything . in technical terms , the cosmological principle states that the universe on large scales is homogeneous and isotropic : it has no preferred places and no preferred directions .if the cosmological principle holds , then the same laws of physics apply everywhere , and when we observe a region of the universe large enough to be statistically representative we can extrapolate its properties to the rest of the cosmos .the second idea is the finite speed of light .when we observe a distant object , we see it as it was when the light left it .this fact turns telescopes into time machines from our vantage point in the present , we can peer back into cosmic history .josiah mcelheny s sculpture _ the center is everywhere _ is based on observations from the sloan digital sky survey ( sdss ) , which has created the largest ever maps of the distant universe .  in detail , the cosmological principle is manifestly wrong .it is different to look up than to look down , different to look to the center of the milky way galaxy than to look outward from our location in its stellar disk , different to look at nearby galaxies like the magellanic clouds or the andromeda nebula than to look elsewhere in the sky .but when we use telescopes to reach far beyond our local neighborhood , the cosmological principle holds remarkably well . while stars are collected in galaxies and galaxies themselves cluster in groups and filaments interweaved with tunnels of emptiness , the average properties of galaxies and clusters and filaments are similar in different regions of the universe .furthermore , when we observe the most distant source of `` light '' that we can see , a background of microwaves that has been traveling freely since the universe became transparent 300,000 years after the big bang , we see that it is astonishingly smooth , implying that the distribution of matter at that time was uniform to within a tiny fraction of a percent .gravity has since amplified primordial fluctuations , the tiny imperfections of that infant universe , into galaxies and larger structures , but the fluctuations themselves were random , so every place in the universe initially had the same chance to become `` interesting '' or `` boring . ''  over the past decade and a half , the sdss has used a dedicated telescope at apache point observatory in new mexico to obtain digital images over 1/4 of the sky and to map the 3-dimensional distribution of more than 2 million galaxies , 1 million stars , and 200,000 quasars .the stars are all members of the milky way at distances of hundreds or thousands of light years ; their separation in time from us is less than a cosmic eyeblink .the galaxies , each a collection of tens or hundreds of billions of stars , span a wide range of distances , from thousands of light years to billions of light years .quasars are the most luminous objects in the universe , powered by hot gas falling onto supermassive black holes , so they can be seen to very large distances .the most distant quasars discovered by the sdss have lookback times of more than 13 billion years , and the light we detect left them less than a billion years after the big bang .  to map millions of galaxies , the sdss observes them using `` fiber plugplates , '' each an aluminum disk in diameter drilled with 640 holes at the locations of objects selected for observation from the digital images .each hole is plugged with an optical fiber , and all 640 fibers are fed back into spectrographs riding on the back of the telescope , which disperse the light into its constituent colors and allow astronomers to infer the properties and distance of each object from subtle patterns of dark and bright lines , which are produced when atoms absorb and emit light at particular wavelengths ._ the center is everywhere _ utilizes a reproduction of one of the sdss plugplates , number 1945 , replacing each optical fiber with a brass suspension rod whose terminating piece represents the astronomical object that the sdss observed through that hole on this plugplate : small glass spheres for stars in the milky way , lamps for the quasars , glass disks for the flattened , spinning galaxies like the milky way , and larger spheres for the rounded `` elliptical '' galaxies that form when gravity drags disk galaxies together and scrambles their stars onto disordered orbits .the length of each rod corresponds to the light - travel distance to the object , with the longest rod in the sculpture representing a light ray that has traveled 12.3 billion years to reach the earth ., where is the lookback time and is present age of the universe computed for a cosmology with , , and . ]  disk galaxies are more common than ellipticals , but the ellipticals are , on average , bigger and brighter , so the sdss telescope can see them to greater distances. scanning downwards from the top of _ the center is everywhere _ , a dense pattern of disks gradually gives way to a sparser sprinkling of ellipticals .quasars are much rarer still , for while most large galaxies contain supermassive black holes , it is only rare , short - lived events that funnel gas toward them and cause them to flare into brilliance . at the peak of its activity , a quasar can outshine its galactic host by a factor of 1000 , so quasars can be detected to the farthest reaches of the universe .the volume mapped by a single plugplate expands like the cone of a lighthouse beam , so at large enough distances it begins to encompass many quasars , rare though they are .stars enter the sdss in many ways : some are observed as standard sources to calibrate measurements of galaxies and quasars , some are mapped in a deliberate pattern to reveal the structure of the milky way , and some are `` contaminants , '' stars with unusual colors that allow them to masquerade as quasars until an sdss spectrum reveals their true identity .= 12.3truecm 0.15truein = 12.3truecm  even a casual inspection of _ the center is everywhere _ shows that galaxies are not randomly distributed through space .the gravity that pulls gas and dark matter into galaxies also pulls the galaxies into groups and clusters , arranged on still larger scales in a web of filaments and walls. a defining goal of the sdss is to measure the clustering of galaxies with exquisite precision and detail , measurements that help to reveal the history of galaxy formation , pin down the geometry , matter , and energy content of the cosmos , and probe the physics of the big bang itself .the cosmic core sample shown in _ the center is everywhere _ is one small chunk of the sdss map of the universe , a random but representative piece of the whole .an individual sdss plugplate covers an area on the sky that is three degrees across , six times the diameter of the full moon , the size of a quarter held at arm s length .the circular plates must overlap so that they do not leave gaps between them , and in its original phase ( see appendix a ) the sdss used more than 2000 plates to map 1/4 of the sky , one quarter - sized patch at a time .an astute viewer with the patience to count will notice that _ the center is everywhere _ has 306 rods , not the expected 640 .the minimum separation of holes in the original sdss plugplate is only , an uncomfortably small size to impose on the cut - glass crystals of a chandelier . _the center is everywhere _circumvents this problem with three compromises : it expands the central region of plate 1945 and trims its edges , it slightly nudges the positions of some holes and the lengths of some rods to create space , and it omits some objects that still ca nt fit .  the full title of mcelheny s sculpture is _study for the center is everywhere_. it is a `` study '' in part because this piece is the first of what may well become a series , with the multitude of sdss plugplates providing an ample library for sculptures that follow common rules but are individually unique .but even a series of 50 such sculptures would still be `` a study '' for the much larger work that could be constructed in principle , with 2000 + chandeliers suspended in an arena - like vault , holding a million glass crystals and lamps to represent the celestial objects that have been mapped by the sdss . andeven this vast conceptual installation would remain `` a study '' : the complete work should take its title seriously and include the maps constructed by astronomers and artists in other , distant galaxies , whose own studies for _ the center is everywhere _ include the milky way as a glimmering disk of glass ._ `` nature is an infinite sphere , whose center is everywhere and whose circumference is nowhere . '' _ the french philosopher blaise pascal wrote this description ( _ penses , 1669 _ ) centuries before the emergence of the modern cosmological model , or the gravitational theory of einstein on which it is based .yet it seems an apt encapsulation of the cosmological principle , of the centerless expansion of the big bang theory , and of our consequent ability to map the universe fairly from an arbitrary point within it . because the universe has a finite age about 14 billion years according to recent observations the size of the _ observable _ universe is , in fact , finite .a galaxy or quasar more than 14 billion light years away is beyond the edge of our cosmic horizon , and it will remain so forever .but just as the slight curvature of the earthly horizon viewed from a ship bespeaks a world far larger than the sailors can see , so astronomical observations ( which , despite increasingly precise measurements , have detected _ no _ curvature of 3-dimensional space ) tell us that the universe is at least hundreds of times larger than the span of our cosmic horizon , probably much larger , and quite possibly infinite .if the cosmological principle holds across an infinite universe , then there are other astronomers mapping their own observable sphere so far from us that we could never communicate , not even in principle .pascal s metaphor has a long history , as described by jorge luis borges in his essay _ the fearful sphere of pascal_. one who took it up was the communist revolutionary louis auguste blanqui , who devoted his imprisonment to writing a cosmological treatise , _ eternity through the stars : an astronomical hypothesis _ ( 1872 ) .on the first page of his book , blanqui repeats and slightly amends pascal s comment : `` _ the universe is a sphere whose center is everywhere and whose surface is nowhere . _ '' blanqui becomes the first to clearly state one of the most bizarre properties of an infinite universe made of constituent atoms and molecules whose variety and possible arrangements are finite .in such a universe , every chance event , and every configuration of matter that can arise from a series of such events , must occur , and not just once , but an infinite number of times .if we take the idea of the infinite seriously , then mathematical reasoning leads us to the dizzying notion that the ( very ) distant universe holds replicas of ourselves , reading the same books , speaking the same words , thinking the same thoughts . . . andnear replicas who do the same thing but in a different language , or with different colored eyes .blanqui s thought experiment is like that of the librarians in the borges story _ the library of babel _ , who conjecture that the library is infinite and conclude that its volumes of seemingly random letters must somewhere include all the works of great literature , and of bad literature , in all variations , over , and over , and over .computations of probabilities in an infinite universe present conceptual and philosophical challenges even today , forming an esoteric and sometimes controversial thread of discussion among contemporary cosmologists and string theorists .the stakes of this discussion are real , for it tells us whether an underlying fundamental theory can , with reasonable probability , explain the world as we see it .observations do not tell us whether the universe is truly infinite , nor whether it remains statistically homogeneous far beyond our horizon , so there are avenues of escape from the replicas that blanqui envisioned .but the mere possibility that we inhabit an infinite universe stocked with infinite replicas disturbs our already troubled senses of individuality and free will .closer to home , our finite observable universe is already enormous , and even the sdss has mapped only a tiny fraction of its contents .space is big and time is long , and these vastnesses can be intimidating .but one can choose instead to marvel at the particularities of nature , at the intricacy of its structures , at the way that gravity and electromagnetism and nuclear forces weave random fluctuations of primordial atoms into a web of galaxies , stars , and planets . on some of these planets , chemistry and biology and evolutionorganize those atoms into beings who can , from their own center of the universe , map the cosmos and begin to understand it .  * acknowledgment *i gratefully acknowledge support from the national science foundation , via grant ast-1009505 .i thank josiah mcelheny for permission to reproduce images of _study for the center is everywhere _ , and for the opportunity to participate in a remarkable collaboration .the sdss was conceived around 1990 , and it began operation in 1998 after nearly a decade of design and construction . in its initial phase ,the sdss used the world s largest digital camera and fiber - fed spectrographs , both mounted on a dedicated 2.5-meter telescope , to obtain deep multi - color images of about 20% of the sky and spectra of nearly a million stars , galaxies , and quasars . in its second phase ( sdss - ii , 2005 - 2008 ) , the sloan collaboration completed the project s original goals and carried out two additional surveys , one a map of stars in the milky way and one a systematic search for supernovae to measure the history of cosmic expansion . in its current phase ( sdss - iii , 2008 - 2014 ) , the collaboration is using the same telescope equipped with upgraded and new spectroscopic instruments to conduct four surveys , of the distant universe , the milky way galaxy , and extra - solar planetary systems .the team is already far along in planning for expanded surveys beyond 2014 .technical descriptions of the sdss include york et al .( 2000 ) for sdss - i , abazajian et al .( 2008 ) for sdss - ii , and eisenstein et al .( 2011 ) for sdss - iii .the `` sloan '' in sdss refers to the alfred p. sloan foundation , which has provided critical funding support to all phases of the sdss .the sdss has also been supported by the participating institutions , by the u.s. national science foundation , department of energy office of science , and national aeronautics and space agency , and by funding agencies of other nations .today the sdss collaboration has more than 500 active scientists from 40 + institutions around the globe .more information about the sdss can be found at the web sites sdss.org and sdss3.org .the public archive of sdss images and spectra is available through skyserver.sdss3.org .josiah mcelheny is an artist who works primarily in glass , though his recent _ oeuvre _ includes films , books , and other media .much of his work is created in his glass - blowing studio in brooklyn , ny . his intellectual interests are wide ranging and include the rise and fall of modernist design and architecture , the history of glass as a material and as an artistic medium , conceptions of the infinite , and contemporary cosmology . among other honors , he was awarded a 2006 macarthur foundation fellowship .david weinberg is a cosmologist and a professor of astronomy at ohio state university .he studies the formation and clustering of galaxies , the structure of the intergalactic medium , and the matter and energy contents of the universe .he was the spokesperson for sdss - ii , and he is the project scientist of sdss - iii .mcelheny and weinberg have collaborated since 2004 on the design of several cosmologically inspired sculptures .the article by weinberg ( 2010 ) describes the scientific and intellectual background to the first four of these collaborative efforts : _ an end to modernity _( 2005 , now in the collection of london s tate modern gallery ) , _ the last scattering surface _ ( 2006 , now in the phoenix art museum ) , _ the end of the dark ages _ ( 2008 , now in a private collection ) , and _ island universe _ ( 2008 ) . the 2012 exhibition _josiah mcelheny : some pictures of the infinite _ , at the boston institute of contemporary art , includes both _ island universe _( previously exhibited in london and madrid ) and the first exhibition of _study for the center is everywhere_. further description of this collaboration can be found in the article by weinberg ( 2011 ) .abazajian , k. , adelman - mccarthy , j. , agueros , m. a. , allam , s. s. , allende prieto , c. , an , d. , et al . , 2009 , `` the seventh data release of the sloan digital sky survey , '' _ the astrophysical journal supplement series _, 182 , 543 .blanqui , l. a. , 1872 , _lternit par les astres : hypothse astronomique _ ,first published in paris by librairie germer ballire and printed by e. martinet .english translation by d. canty , edited by j. mcelheny , published in 2012 by the donald young gallery ( chicago ) .eisenstein , d. j. , weinberg , d. h. , agol , e. , aihara , h. , allende prieto , c. , anderson , s. f. , et al ., 2011 , `` sdss - iii : massive spectroscopic surveys of the distant universe , the milky way galaxy , and extra - solar planetary systems , '' _ the astronomical journal _ , 142 , 72 .weinberg , d. h. , 2010 , `` from the big bang to the multiverse : translations in space and time , '' in _ josiah mcelheny : a prism _ , eds . l.neri & j. mcelheny , skira / rizzoli books ( new york ) .available as arxiv:1006.1012 .

Abstract: _ the center is everywhere _ is a sculpture by josiah mcelheny , currently ( through october 14 , 2012 ) on exhibit at the institute of contemporary art , boston . the sculpture is based on data from the sloan digital sky survey ( sdss ) , using hundreds of glass crystals and lamps suspended from brass rods to represent the three - dimensional structure mapped by the sdss through one of its 2000 + spectroscopic plugplates . this article describes the scientific ideas behind this sculpture , emphasizing the principle of the statistical homogeneity of cosmic structure in the presence of local complexity . the title of the sculpture is inspired by the work of the french revolutionary louis auguste blanqui , whose 1872 book _ lternit par les astres : hypothse astronomique _ was the first to raise the spectre of the infinite replicas expected in an infinite , statistically homogeneous universe . puzzles of infinities , probabilities , and replicas continue to haunt modern fiction and contemporary discussions of inflationary cosmology .


with ever increasing global population and even faster densification of various large metropolitan areas of the world , mass transit systems are becoming more important .improved transit systems are also important for keeping personal cars off of congested road networks , thus addressing climate change concerns and making future switch to cleaner energy source easier .urban planners are hard at work designing faster , cheaper , safer and more comfortable transit systems .most often local and federal governments are in charge of building transit systems .if we view transit systems as a public utility then this government control is reasonable .but it also means that there is almost no competition in most cities .it is widely believed that for most businesses competition may improve efficiency and quality of service .one area where fierce competition has helped reduce inefficiencies is electronic capital markets . global stock exchanges and market placesare more at sync and bid - ask spreads are low .one core principle that guides such optimization is the elimination of arbitrage or riskless profit making.  the goal of this paper is to investigate whether there are pricing inefficiencies in mass transit systems that can lead to arbitrage and ask how we can improve transit fares for commuters . as a case study we looked at san francisco bay area rapid transit ( bart ) system , which is the fifth largest transit system by ridership in the us .we also took a cursory look at washington dc metrorail , which is the second largest system in the us .a motivating example is the case when one individual is traveling from millbrae station , a suburb south of san francisco , to embarcadero station which is downtown san francisco , and at the same time a second individual is traveling from glen park station , a residential area in san francisco , to berkeley station where university of california berkeley is located .the two tickets cost ( according to http://www.bart.gov/sites/default/files/docs/bart%202014%20fare%20chart_tab.pdf[2014 fare chart ] ) 4.20 respectively .but if during the segment between glen park station and embarcadero station the two travelers agree to exchange their tickets the cost becomes 1.85 .so from a total cost of 1.75 or 20% .another similar example comes from washington dc metrorail .if one individual is traveling from vienna / fairfax station to metro center station on the orange line and another individual is traveling from rosslyn station to new carrollton station on the same train then during peak hours they pay 4.9 .but if the travelers decide to swap tickets they pay 2.1 instead. so the saving is 1 to be gained .the full list of these 4,666 pairs of trips with net arbitrage amount and percentage is available at this https://github.com/asifhaque/transit-arbitrage/blob/master/data/sf/arbitrage.txt[`github repo file ` ] ] .computing such pairs involves exhaustively finding overlapping paths between trips where the cost would be lower .given that transit graphs are often spanning trees , even a brute force solution has complexity where is the number of stations in the system. for bart = 44 and computation finishes in under a minute on a laptop .source code , input and output data is available at https://github.com/asifhaque/transit-arbitrage[`github.com/asifhaque/transit-arbitrage ` ]  if bart authorities release anonymized data of every trip for users traveling through the system it would be very interesting to compute the total amount in dollars that san francisco bay area commuters can save every day.  it would be interesting to explore washington dc metrorail in detail as well .since it is a larger system with peak and off - peak rates , arbitrage strategies could be more complicated .preliminary investigation exposes possibility of arbitrage .fig [ fig : vienna - carrollton ] shows fares from vienna / fairfax station towards new carrollton on the orange line of washington dc metrorail .we can see that the price structure is indeed very similar to the blue line in fig [ fig : dist - vs - fare ] and what we have seen for bart .the initial steep part passes through falls church suburbs leading to slight flattening around george mason university ( station 5 ) .there is another steep part leading to dc city center around station 10 .heading out towards the suburbs prices are essentially flat for commuters coming all the way .in this paper we have explored basics of transit fare arbitrage and analyzed bart fare structure both qualitatively and quantitatively via exhaustive computation . our study highlights the need for careful design of pricing models for transit systems .one interesting direction that might lead to an efficient fare system is if tickets are all electronic , ideally via a smartphone app , that third parties can manage to optimize inidividual trips . in recent years barthas moved from paper tickets towards clipper cards ( nfc tags ) .data is encrypted on these cards and can be read by any nfc reader but not written to except for bart machines .if in future we start using smartphone nfc capabilites ( google wallet for example ) and allow third parties to dynamically swap account profile on the smartphone app then arbitrage will be technically very easy. it may even allow arbitrage between routes that do not have overlapping paths and ultimately force the prices to be arbitrage free and thus efficient .we can imagine companies like uber and lyft managing such apps to provide commuters with a uniform payment interface encompassing ride shares and mass transit .

Abstract: transit fare arbitrage is the scenario when two or more commuters agree to swap tickets during travel in such a way that total cost is lower than otherwise . such arbitrage allows pricing inefficiencies to be explored and exploited , leading to improved pricing models . in this paper we discuss the basics of fare arbitrage through an intuitive pricing framework involving population density . we then analyze the san francisco bay area rapid transit ( bart ) system to understand underlying inefficiencies . we also provide source code and comprehensive list of pairs of trips with significant arbitrage gain at https://github.com/asifhaque/transit-arbitrage[`github.com/asifhaque/transit-arbitrage ` ] . finally , we point towards a uniform payment interface for different kinds of transit systems .


speech recognition proved to be successful in enormous applications in the last few decades .tthe cognitive infocommunications ( coginfocom ) systems ties in closely with the patterns and speech recognition area since the user and the coginfocom systems can interact through a human computer communication  .+ there has been a considerable improvement in speech applications since it is closely related to the information and communications technology and cognitive science problems .  despite the considerable progress in speech researches , the robustness of speech recognition systems still slight due to many factors such as large data , noisy environments , speaker voice , etc .unfortunately , many speech recognition systems have their limits to accomplish the human performance .+ for example , a phoneme recognition system is based on a sequence of phones but those phones bring the understanding and the confusion with the neighboring phonemes .thus , many studies in the speech recognition develop techniques that provide into the speech recognition systems greater levels of knowledge of the language .indeed , the relationship between speech recognition and cognitive capacity proved to have a direct impact on the human - interaction systems . buthow is the interaction between speech and cognitive science in the development of speech recognition systems ?+ in fact , the cognitive model based on the speech recognition systems have to better focusing in the descriptions input such as the raw acoustic signal in order to boost the accuracy of the recognition system . in this context , this paper tries to improve the performance of a speech recognition system based on a raw acoustic input recording from a microphone .several speakers ( female and male ) pronounce few sentences but each speaker has its own behavior , accent , energy , noise , etc .those cognitive factors make it difficult to the robustness of the speech recognition system .+ in the automatic speech recognition ( asr ) field , the choice of the learning algorithm for building of any asr system is a crucial step since the success of the recognition task depends essentially on learning stage .recently , the boosting have been proved to be an efficient method for improving the performance of different classifiers .therefore , this technique is used to combine a collection of component classifiers ( called also weak classifiers ) , to form a single `` strong '' classifier .it consists in calling repeatedly the component classifier on different weights over the training samples and adaptively adjusting these weights after each boosting iteration .+ adaboost is the most popular method of boosting .the great success of adaboost can be attributed to its ability to maximize the margin on a training set , which lead to improve the performance of the classifier .the efficiency of adaboost is closely related to the component classifier used .since the main objective of adaboost is to enhance the learning performance of a given weak classifier , then combing adaboost with a strong classifier may not necessarily be optimum choice and it may be going against the gain of the boosting principle .furthermore , the choice of the learning algorithm , generally , affect the recognition rates . but how to distinguish between a `` weak '' and a `` strong '' learner algorithm ? + we propose this study to emphasize the notion of `` the weak and strong learner '' ; svm and c4.5 are two strong algorithms which constitutes our base component classifiers .in particular , we would observe the behaviour of svm with adaboost .the remaining parts of this paper is organized as follows : in section [ sec:1 ] , the main idea of adaboost is introduced . in section [ sec:2 ] , the learning algorithms used in this study are presented ; the architecture of our asr system is proposed in section [ sec:3 ] ; experimental setup and results are described in sections [ sec:4 ] .the conclusion is made in section [ sec:6 ] .the boosting method was inspired by on - line learning algorithm called hedge which allocate weights to a set of hypothesis used to predict the outcome of any system .recently , boosting method has been quite successfully applied on real - world applications and it was mostly used on the speech recognition field .the most and widely used boosting algorithm is adaboost .+ adaboost ( adaptive boosting ) , an iterative algorithm , was originally introduced by feund and schapire on 1995  .+ if the applied learning algorithm had a low performance , adaboost algorithm generates a sequentially weighted set of weak classifiers in order to create new classifiers which are more operational on the training data .hence , the adaboost algorithm multiple iteratively classifiers to improve the classification accuracies of many different data sets compared to the given best individual classifier .+ the main idea of adaoost is to run repeatedly a given weak learning algorithm in different probability distributions , , over the training data .this distribution is initially set uniform .+ in the meantime , adaboost calls the weak learner algorithm repeatedly in a series of cycles .then , it assigns higher weights to the misclassified samples by the current component classifier(at cycle t ) , in the hopes that the new weak classifier can reduce the classification error by focusing on it .meanwhile , lower weights will be assigned to the correctly classified samples  .thereafter , the distribution is updated after each cycle . in the end , hypothesis produced by the weak learner from each cycle are combined into a single `` strong '' hypothesis  .+ the importance of adaboost lies in the component classifiers which is systematically have an accuracy slightly higher than 50% .this means that the component classifiers have to be better than a random estimation .+ briefly , adaboost is a meta - learning method that tries to build a `` strong '' learning algorithm based on a group of `` weak '' classifiers .it must be pointed out that boosting has been very successful for solving two - class classification problems .+ meanwhile , to achieve multi - class classification , most algorithms have to convert the multi - class problem to a multiple binary classification problems .our asr system will use adaboost.m1 .+ since this paper discuss an hybrid of the learning algorithm with adaboost , we will present an overview of other related studies that used adaboost in cognitive systems . in the few past years, several studies combining adaboost and cognitive systems have been developed to take advantage of the adaboost algorithm to improve the system s performance .chakraborty present in an expert cognitive system which use adaboost to boosts the performance of an ensemble of classifiers .the empirical comparison of his study shows that hybrid learner based adaboost outperforms the single weak learner .+ stanciulescu et al . used adaboost algorithm in order to improve the real - time object detection in complex robotics problem .experimental results of this study on a car database show that the boosted classifier improve the results of the vehicle - detection application .+ on the other hand , lee and al . used adaboost for the text detection in natural scene to enhance the detection system .+ for a driver s cognitive distraction detection problem , the authors used adaboost to improve the performance for detection of driver distraction . based on experimental results , the authors shows the capability of adaboost to enhance the accuracy of a problem based on the detection of state of cognitive distraction .+ adaboost was combined with svm for a triaxial accelerometer - based fall detection problem in .the experimental results proves that the proposed method adaboost - svm gives optimal results compared to those with the single method .the adaboost - svm produces , also , the the lowest false alarm rate and the detection results as well as the highest accuracy results of their study .the principal aim of the learning algorithm is to extract regularities from sets of samples .they are consisting of several algorithms that improve automatically the system through experience .+ in this paper , we are interested by the supervised learning since it allows to generate function that maps inputs to desired outputs . + in the last decades, different learning algorithms were applied to identify and verify the speech .there is several algorithms that were mostly used in the asr such as decision tree , lda , svm , the baseline system , etc .+   a support vector machine ( svm ) is a learning algorithm for pattern recognition and regression problems whose approaches the classification problem as an approximate implementation of the structural risk minimization ( srm ) induction principle .+ svm approximates the solution to the minimization problem of srm through a quadratic programming optimization . it aims to maximize the margin which is the distance from a separating hyperplane to the closest positive or negative sample between classes . +a subset of training samples is chosen as support vectors .they determine the decision boundary hyperplane of the classifier .based on this principle , the svm adopts a systematic approach to find a linear function that belongs to a set of functions with lowest vc dimension ( the vapnik chervonenkis dimension measure the capacity of a statistical classification algorithm ) .+ applying a kernel trick that maps an input vector into a higher dimensional feature sapce , allows to svm to approximate a non - linear function and and . in this paper , we use svm with the radial basis function kernel ( rbf ) .c4.5 is a learning algorithm used to generate a decision tree developed by ross quinlan .the decision tree c4.5 is an extension of quinlan s earlier id3 algorithm ( iterative dichotomiser 3 ) .+ just like id3 , c4.5 employs a `` divide and conquer '' strategy and uses the concept of information entropy to compute builds decision trees from a set of training ( the split criteria ) the training data is a set of already classified samples .each sample is a vector where represent attributes or feature of the sample .+ the training data is augmented with a vector represent the class to which each sample belongs .+ at each node of the tree , c4.5 chooses one attribute of the data that most effectively splits its set of samples into subsets enriched in one class or the other .its criterion is the normalized information gain ( difference in entropy ) that results from choosing an attribute for splitting the data .the attribute with the highest normalized information gain is chosen to make the decision .+ with the adaptively boosted c4.5 decision tree classifiers , very high degree of accuracy can be achieved in asp field .the architecture of our phoneme recognition system is described in this section .the proposed system aims to compare the performance of adaboost with svm - based component classifier and the performance of adaboost with decision tree c4.5-based component classifier on a phoneme recognition task , ( see fig . [ fig111 ] ) .+   +   the proposed phoneme recognition system passes through several stage with the transformation of the speech samples to spectrogram and then to mfcc spectrum by applying the spectral analysis .then , we proceed to the the phoneme segmentation to constitute seven sub - phoneme sets .the finale stage consists on applying the proposed algorithms for the phoneme recognition problem , see figure [ fig111 ] .+ this system aims to use two different algorithms as component classifier in adaboost .then , the comparison of error generalization is made in order to see the ability of adaboost with those two classifiers .the experiments with our asr system consists in recognizing which identity of phoneme which been tested ( i.e. aa , ae , ih , etc ) .+ we split beforehand the phonemes into 7 groups ( vowels , stops , nasals , fricatives , affricates , semi - vowels , others(silence)) .as discussed in the previous section , the first setp in a asr system is the feature extraction .it converts the speech waveform to a set of parametric representation .hence , we have used the mel frequency cepstral coefficients ( mfcc ) feature extractor . + in 1980 , davis and mermelstein developed the mfcc features for speech classification systems .it consists on the cepstral coefficients which are produced by the mel - frequency warped fourier transform function . + the system that we present in this paper use the speech samples extracted from the timit corpus .moreover , for the nonlinear svm approach with the `` one - against - one '' strategy , we choose the rbf ( gaussian ) kernel trick , this choice was made after a previous study done on our data sets with different kernel tricks ( linear , polynomial , sigmoid ) .+ the experiments using svm are done using libsvm toolbox .the table [ tab : tablee1 ] recapitulate our main choice of experiments conditions :  .experimental setup [ cols= " < , < " , ]   [ tab : tablee1 ]in this section , svm and decision tree c4.5 are compared with the commonly used adaboost , which takes svm and decision tree c4.5 as component classifiers .+ at this stage of experiments , we investigate to find the impact of adaboost on the two learning classifiers selected .  for the phoneme recognition systems ,we compare the performance of our component classifier in adaboost and single classifiers on 7 data sets which are vowels , semi - vowels , stops , others , nasals , fricatives , affricates .the final performance of each algorithm on a data set is the average of the results over the 7 data sets . + it must be pointed out that the number of iteration of adaboost for the recognition system was fixed to 25 . in general , the boosted classifier performs well even with only 10 iterations .l||cccc  * classifiers * & * svm * & * adaboostsvm * & * c4.5 * & * adaboostc4.5 * +  [ 1]**vowel * & [ 1]*44.74 & [ 1]*45.83 & [ 1]*72.95 & [ 1]*75.80 +  + [ 0]**semi - vowel * & [ 0]*18.55 & [ 0]*22.38 & [ 0]*38.91 & [ 0]*27.62 +  + [ 0]**stops * & [ 0]*45.72 & [ 0]*45.99 & [ 0]*64.62 & [ 0]*68.45 +  + [ 0]**others * & [ 0]*14.93 & [ 0]*15.97 & [ 0]*18.40 & [ 0]*16.32 +  + [ 0]**nasal * & [ 0]*39.46 & [ 0]*41.57 & [ 0]*61.45 & [ 0]*48.80 +  + [ 0]**fricative * & [ 0]*21.02 & [ 0]*26.14 & [ 0]*44.51 & [ 0]*29.17 +  + [ 0]**affricate * & [ 0]*21.43 & [ 0]*33.33 & [ 0]*45.24 & [ 0]*33.33 +  + * average * & 29.40 & 32.95 & 49.44 & 42.78 +  [ tab : tab1 ]  the table [ tab : tab1 ] describes generalization errors of the four algorithms for the given 7 data sets with -middle frames which are vowel , semi - vowel , fricative , affricate , nasal , silences and stops .+ the empirical results present the performance of the phoneme recognition system with the singles classifiers svm and c4.5 and the combined classifiers .the database is composed by 70% of learning data and 30% of test data which are used for the validation .+ since the generalization errors of adaboostc4.5 are less than those of c4.5 on these 7 data sets .we can conclude that adaboostc4.5 performs better than c4.5 ( i.e. nasal : 61% vs 48% ) .+ in semi - vowel , others , nasal , fricative , affricate , adaboostc4.5 gets better accuracy compared with those generates by c4.5 ( i.e. the accuracy of fricative data sets improves about 15% ) .+ in turn , the same conclusion can not be drawn from table [ tab : tab1 ] for the single svm - rbf and adaboostsvm .we observe that the adaboostsvm performs similarly or worse than the single svm - rbf .we think that forcing the strong svm classifiers ( svm with its best parameters ) to concentrate on the very hard samples with too much emphasis is the cause of performance degradation in adaboostsvm algorithm . +this case is also observed in which show that adaboost with strong classifier component classifier is not effective .+ for adaboostsvm , the accuracy have been slightly better on vowel , stops and affricate data sets and the improvement reach about 1,8% . while , for the rest of data sets used , adaboostsvm performs slightly worse than single svm and the declination reach about 4% . + from table [ tab : tab1 ] , we , also , observed that svm outperforms both c4.5 and adaboost c4.5 , in general , on these data sets .furthermore , for svm we set a small value of and also the most suitable for our data ( =0.008 ) , which make the svm classifier stronger .+ thus , adaboost become inefficient because the errors of these component classifiers are highly correlated .hence , the use of a suitable gamma for svm component classifier un adaboost leads to lower the performance of adaboostsvm for phoneme recognition .+ we would like to emphasize that the purpose of our experiments is not to argue that svm - rbf performs better than the decision tree c4.5 and the boosted c4.5 , but rather to illustrate that svm and c4.5 are two strong algorithm , but with svm optimization problem has been encountered since the performance degradation is the natural expectation of the hybrid adaboost and the strong svm - rbf to the multi - class case .+ in the last decades , some experiments were carried out in order to better understand why boosting sometimes leads to a deterioration in generalization performance .freund and schapire put this down to overfitting a large number of trials t ( t for adaboost iteration number ) which allows to composite classifier to become very complex and .+ besides these , boosting try to build a strong classifier from weak classifiers .however , if the performance of the classifier is better than random estimation , then boosting may not result in a strong classifier and this method would be going against the gain of the boosting principle and not achieve the desired results .in this paper , we have used adaboost as classifier in order to build a phoneme recognition system .we combined adaboost algorithm with both svm and c4.5 classifiers in order to show the impact of this algorithm on the performance of recognition system .for the this phonemes recognition system we have shown that adaboostc4.5 have on error rate lower than the single c4.5 .but , single svm - 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Abstract: the use of digital technology is growing at a very fast pace which led to the emergence of systems based on the cognitive infocommunications . the expansion of this sector impose the use of combining methods in order to ensure the robustness in cognitive systems . + boosting is a technique for combining many weak classifiers to form one high - performance prediction rule to improve the performance of any given learning algorithm . in theory , boosting can be used to reduce the error of the learning algorithm which generates learners that needs to be better than random guessing . adaboost is the most used boosting algorithm . support vector machines ( svms ) and adaptive boosting ( adaboost ) are two successful classification methods which are essentially similar as they both try to maximize the minimal margin on a training set . in this paper , we will investigate the impact of adaboost on the supervised algorithm svm for a multi - class phoneme recognition problem . this task may be complex since svm is not an easy classifier to train and so , adaboostsvm may not be viable . furthermore , we compare the recognition rates to other commonly used adaboost methods , such as decision tree c4.5 . from the different phoneme datasets , we shall show that the single svm - rbf outperforms decision tree c4.5 , the adaboostc4.5 and even the adaboost svm - based component classifier .  to experiment adaboostsvm , we use the phoneme datasets from timit corpus and mfcc feature representations .   svm , adaboost , optimization , c4.5 , phoneme