Patent Publication Number: US-8972770-B1

Title: Systems and methods for conducting experiments on applications

Description:
FIELD 
     The subject technology generally relates to conducting experiments and, in particular, relates to systems and methods for conducting experiments on applications. 
     BACKGROUND 
     When providing an application to a population of users, it may be useful to allow users to consent to reporting anonymous usage statistics of the application so that these usage statistics may be used to improve the application. In this regard, an experiment to test different variations of the application can be conducted (e.g., by assigning different variations to different users). The anonymous usage statistics of the users who consented can be compared to one another in order to determine which variation provided better performance and therefore can be used to improve the application. However, the more experiments that are conducted and/or the fewer users there are may mean that a particular user can be inadvertently assigned a unique set of variations (e.g., different from other users&#39; assigned variations), thereby potentially making this particular user more uniquely identifiable. 
     SUMMARY 
     According to various aspects of the subject technology, a system for conducting a set of experiments on an application having a plurality of users is provided. Each experiment is identified by a respective experiment identification (ID) and is associated with a respective group of experimental variations of the application. The system comprises an entropy source module configured to assign a user group number to a designated one of the plurality of users. The user group number is less than or equal to an entropy cap. The entropy cap is less than an expected entropy associated with the set of experiments. The expected entropy represents a total number of different states of the set of experiments. Each of the different states comprises a respective experimental variation of each experiment. The system also comprises an experiment module configured to determine a designated one of the set of experiments to be conducted on the application in connection with the designated user. The designated experiment is identified by a designated experiment ID and is associated with a designated group of experimental variations of the application. The experiment module is configured to assign a designated one of the designated group of experimental variations to the designated user based on the user group number. 
     According to various aspects of the subject technology, a computer-implemented method for conducting a set of experiments on an application having a plurality of users is provided. Each experiment is identified by a respective experiment identification (ID) and is associated with a respective group of experimental variations of the application. The method comprises assigning a user group number to a designated one of the plurality of users. The user group number is less than or equal to an entropy cap. The entropy cap is less than an expected entropy associated with the set of experiments. The expected entropy represents a total number of different states of the set of experiments. Each of the different states comprises a respective experimental variation of each experiment. The method also comprises determining a designated one of the set of experiments to be conducted on the application in connection with the designated user. The designated experiment is identified by a designated experiment ID and is associated with a designated group of experimental variations of the application. The method also comprises assigning a designated one of the designated group of experimental variations to the designated user based on the user group number and the designated experiment ID. 
     According to various aspects of the subject technology, a machine-readable medium encoded with executable instructions for a method of conducting a set of experiments on an application having a plurality of users is provided. Each experiment is identified by a respective experiment identification (ID) and is associated with a respective group of experimental variations of the application. The method comprises randomly assigning a user group number to a designated one of the plurality of users. The user group number is greater than zero and less than or equal to an entropy cap. The entropy cap is less than an expected entropy associated with the set of experiments. The expected entropy represents a total number of different states of the set of experiments. Each of the different states comprises a respective experimental variation of each experiment. The method also comprises determining a designated one of the set of experiments to be conducted on the application in connection with the designated user. The designated experiment is identified by a designated experiment ID and is associated with a designated group of experimental variations of the application. The method also comprises assigning a designated one of the designated group of experimental variations to the designated user based on the user group number and the designated experiment ID. The method also comprises tagging usage statistics of the designated user with the designated experimental variation. 
     Additional features and advantages of the subject technology will be set forth in the description below, and in part will be apparent from the description, or may be learned by practice of the subject technology. The advantages of the subject technology will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide further understanding of the subject technology and are incorporated in and constitute a part of this specification, illustrate aspects of the subject technology and together with the description serve to explain the principles of the subject technology. 
         FIGS. 1A and 1B  illustrate an example of an application on which a set of experiments can be conducted, in accordance with various aspects of the subject technology. 
         FIG. 2  illustrates an example of an arrangement in which a set of experiments may be conducted on an application, in accordance with various aspects of the subject technology. 
         FIG. 3  illustrates an example of a system for conducting a set of experiments on an application, in accordance with various aspects of the subject technology. 
         FIG. 4  illustrates an example of a method for conducting a set of experiments on an application, in accordance with various aspects of the subject technology. 
         FIG. 5  conceptually illustrates an electronic system with which any implementations of the subject technology are implemented. 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth to provide a full understanding of the subject technology. It will be apparent, however, that the subject technology may be practiced without some of these specific details. In other instances, structures and techniques have not been shown in detail so as not to obscure the subject technology. 
       FIGS. 1A and 1B  illustrate an example of application  100  on which a set of experiments can be conducted, in accordance with various aspects of the subject technology. Although application  100  is shown in  FIGS. 1A and 1B  as a web browser, application  100  can be other types of applications such as productivity tools (e.g., word processing programs, calendar programs, database programs, etc.), social networking programs, multimedia programs (e.g., for video, audio, and/or image editing and/or playback, etc.), communication programs (e.g., email programs, phone/contacts programs, texting programs, etc.), and the like. 
     The set of experiments can be conducted on application  100  in order to test different variations of the application (e.g., by assigning different variations to different users). Users of application  100  may be provided with an opportunity to control whether any activity of the users may be anonymously reported as usage statistics to a provider of application  100  in order to improve application  100 . Should a user consent, this user&#39;s usage statistics may be tagged with the specific variation assigned to this user and then be reported to the provider. The anonymous usage statistics of the users can be compared to one another in order to determine which variation provided better performance and therefore can be used to improve application  100 . The usage statistics, for example, can include information such as the number of tabs that were open, the use of any particular settings, the length of time spent on performing an activity, whether the user signed in to a particular service, etc. 
     For example, one experiment that can be conducted on application  100  is to determine the effect of having a “+” sign depicted on new tab button  102   a  (e.g., shown in  FIG. 1A  and referred to as variation A) versus having no “+” sign depicted on new tab button  102   b  (e.g., shown in  FIG. 1B  and referred to as variation B). This experiment may be identified by an experiment identification (ID) of  1  and be associated with the group of experimental variations A and B. Another experiment that can be conducted on application  100  is to determine the effect of having striped lines depicted on settings button  104   a  (e.g., shown in  FIG. 1A  and referred to as variation C) versus having a wrench depicted on settings button  104   b  (e.g., shown in  FIG. 1B  and referred to as variation D). This experiment may be identified by an experiment ID of  2  and be associated with the group of experimental variations C and D. Another experiment that can be conducted on application  100 , for example, is to determine the effect of having a sign-in reminder  106  (e.g., shown in  FIG. 1A  and referred to as variation E) versus having no sign-in reminder (e.g., shown in  FIG. 1B  and referred to as variation F). This experiment may be identified by an experiment ID of  3  and be associated with the group of experimental variations E and F. Although only several experiments with two variations each are described, any number of experiments with any number of variations can be conducted on application  100 . 
     To conduct all three experiments, a particular user may be assigned either variation A or variation B from experiment  1 , either variation C or variation D from experiment  2 , and either variation E or variation F from experiment  3 . For example, the user may be assigned variations A, C, and E. Thus, this user may be considered as assigned to a state of A, C, and E. The following is a list of all the different states that a user may be assigned to for experiments  1 ,  2 , and  3 : 
     ACE 
     ACF 
     ADE 
     ADF 
     BCE 
     BCF 
     BDE 
     BDF 
     Thus, the total number of different states of experiments  1 ,  2 , and  3  is 8. This total number may be referred to as the expected entropy associated with the set of experiments conducted on application  100 . However, the problem with conducting experiments in this manner is that the more experiments that are conducted and/or the fewer users there are may mean that a particular user can be inadvertently assigned a unique state, thereby potentially making this particular user more uniquely identifiable. For example, if the number of users of application  100  is less than the expected entropy (e.g., there are only five users of application  100 ), then each of these users may potentially be assigned a unique state, and therefore may be potentially identified. 
     According to various aspects of the subject technology, systems and methods are provided for conducting a set of experiments on application  100  while reducing the risk of uniquely identifying a particular user. This can be achieved by capping the expected entropy associated with the set of experiments with an entropy cap such that each user cannot be assigned a unique state. In other words, the expected entropy may be capped such that it is likely that more than one user can be assigned the same state. A user group number that is less than or equal to the entropy cap may be randomly assigned to a particular user. Since this user group number is not unique to this particular user, an experimental variation can be assigned to this user based on the user group number, thereby minimizing the risk of uniquely identifying this particular user. 
       FIG. 2  illustrates an example of arrangement  200  in which a set of experiments may be conducted on application  100 , in accordance with various aspects of the subject technology. Arrangement  200  includes one or more servers  206  (e.g., servers  206   a  and  206   b ) and client devices  202  (e.g., client devices  202   a ,  202   b ,  202   c ,  202   d , and  202   e ) connected over network  204 . Network  204  can include, for example, any one or more of a personal area network (PAN), a local area network (LAN), a campus area network (CAN), a metropolitan area network (MAN), a wide area network (WAN), a broadband network (BBN), a peer-to-peer network, an ad-hoc network, the Internet, and the like. Further, network  204  can include, but is not limited to, any one or more network topologies such as a bus network, a star network, a ring network, a mesh network, a star-bus network, tree or hierarchical network, and the like. 
     Servers  206 , for example, may provide application  100  to a population of users using client devices  202 . Client devices  202  and servers  206  can be any electronic device having processing hardware, memory, and communications capability necessary to perform some or all of the operations disclosed herein. Client devices  202 , for example, can be desktop computers (e.g., client device  202   b ), laptop computers (e.g., client device  202   d ), tablet computers (e.g., including e-book readers such as client device  202   a ), mobile devices (e.g., smartphones or personal digital assistants such as client device  202   c ), set top boxes (e.g., for a television with one or more processors coupled thereto and/or embedded therein such as client device  202   e ), video game consoles, and/or any other electronic devices having memory, processing hardware, and communications capabilities for performing one or more operations according to certain aspects of this disclosure. 
     In some aspects, servers  206  may randomly assign user group numbers to client devices  202  and then assign different variations of application  100  to client devices  202  based on the assigned user group numbers in order to conduct the set of experiments on application  100 . For example, servers  206  may assign a user group number of  1  to client device  202   a , a user group number of  2  to client devices  202   b  and  202   d , a user group number of  3  to client device  202   c , and a user group number of  4  to client device  202   e . Based on these user group numbers, servers  206  may provide variation A to client devices  202   a  and  202   c , and provide variation B to client devices  202   b ,  202   d , and  202   e . Usage statistics of client devices  202 , which may be tagged with the different variations of application  100 , may be reported back to servers  206  over network  204 , thereby allowing a provider of application  100  to determine how to improve application  100  based on this information. 
       FIG. 3  illustrates an example of system  300  for conducting a set of experiments on application  100 , in accordance with various aspects of the subject technology. System  300 , for example, may be part of client devices  202  and/or servers  206 . System  300  comprises entropy source module  302 , experiment module  304 , and labeling module  306 . These modules may be in communication with one another. In some aspects, the modules may be implemented in software (e.g., subroutines and code). In some aspects, some or all of the modules may be implemented in hardware (e.g., an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a Programmable Logic Device (PLD), a controller, a state machine, gated logic, discrete hardware components, or any other suitable devices) and/or a combination of both. 
     Additional features and functions of these modules according to various aspects of the subject technology are further described in the present disclosure. 
       FIG. 4  illustrates an example of method  400  for conducting a set of experiments on application  100 , in accordance with various aspects of the subject technology. In particular, method  400  may be implemented to assign a particular variation of application  100  to a user while reducing the risk of uniquely identifying this user. System  300 , for example, may be used to implement method  400 . However, method  400  may also be implemented by systems having other configurations. Although method  400  is described herein with reference to the examples of  FIGS. 1A ,  1 B,  2 ,  3 , and  5 , method  400  is not limited to these examples. 
     According to step S 402 , entropy source module  302  assigns a user group number to a particular one of the plurality of users of application  100  (e.g., a designated user). As discussed above, the user group number may be less than or equal to an entropy cap that caps the expected entropy associated with the set of experiments, thereby making the user group number not unique to the designated user. In this regard, an experimental variation can be assigned to the designated user based on the assigned user group number, thereby minimizing the risk of uniquely identifying this user. 
     For the purpose of illustration, assume that there are only 8 users of application  100 , and that experiments  1 ,  2 , and  3  are to be conducted on application  100 . As discussed above, the expected entropy associated with these experiments is 8 (e.g., 8 total different states that a user may be assigned to). Since there are only 8 users of application  100 , it may be possible that each user is assigned a unique state. The entropy cap, however, may be used to address this problem. The entropy cap may be a number (e.g., an integer) that is less than the expected entropy. For the purpose of illustration, assume that the entropy cap in this example is 4. The user group number, which may be a number (e.g., an integer) greater than zero and less than or equal to the entropy cap, may then be randomly assigned to each of the 8 users. Because the user group number is less than or equal to the entropy cap, it is likely that more than one of the 8 users may share the same user group number. For example, two users may share a user group number of  1 , two other users may share a user group number of  2  , two other users may share a user group number of  3 , and two other users may share a user group number of  4 . Thus, the assigned user group number is not unique to a particular user, including the designated user. 
     According to step S 404 , experiment module  304  determines a particular one of the set of experiments to be conducted on application  100  in connection with the designated user. For example, experiment module  304  may select either experiment  1 , experiment  2 , or experiment  3  to be conducted on application  100  in connection with the designated user. In some aspects, the provider of application  100  may select the experiment to be conducted on application  100 . For ease of discussion, the selected experiment may be referred to as the designated experiment. 
     According to step S 406 , experiment module  304  assigns one of the experimental variations associated with the designated experiment to the designated user based on the assigned user group number. Because the assigned user group number is not unique to the designated user, the experimental variation that is assigned to the designated user may also not be unique to the designated user, thereby minimizing the risk of uniquely identifying the designated user. 
     According to certain aspects, experimental module  304  may assign one of the experimental variations associated with the designated experiment to the designated user based on the assigned user group number as well as the experiment ID of the designated experiment, which may allow for a specific variation from the designated experiment to be assigned to the designated user. For example, assume that the designated experiment is experiment  1 , and the assigned user group number is  3 . Thus, experiment module  304  may assign either variation A or variation B to the designated user based on the assigned user group number  3  and the experiment ID  1 . 
     In some aspects, experiment module  304  may determine which variation to assign the designated user using a function that can increase the likelihood that each variation of the designated experiment may be assigned to the plurality of users using application  100 . For example, the function may increase the likelihood that if variation A is assigned to the designated user, the other variation, variation B, may be assigned to a different user, thereby ensuring that experiment  1  can be conducted on application  100 . According to certain aspects, such a function may be given by: 
     (X+Y) modulo Z, 
     where X=the designated experiment ID, 
     Y=the user group number, and 
     Z=a total number of experimental variations associated with the designated experiment. 
     The total number of different results of this function for a given experiment may be the same as the number of variations associated with that experiment. In this regard, each variation associated with an experiment may be assigned to a unique result of this function, and if such a result is computed by the function, experiment module  304  may assign the variation corresponding to the computed result to the designated user. For example, suppose variation A is assigned to a unique result of 0 computed by the function for experiment  1 , while variation B is assigned to a unique result of 1 computed by the function for experiment  1 . Using the values from the previous illustration, X=1 (e.g., from the experiment ID of  1 ), Y=3 (e.g., from the assigned user group number), and Z=2 (e.g., since experiment  1  is associated with two variations). Thus, the result of the function using these values is 0. Since variation A is assigned to the unique result of 0, experiment module  304  may assign variation A to the designated user. If the designated user were assigned a different user group number such as  2 , then the result of the function would be 1. In this case, experiment module  304  would assign variation B to the designated user since variation B is assigned to the unique result of 1. 
     According to step S 408 , labeling module  306  may tag usage statistics of the designated user with the assigned experimental variation. For example, labeling module  306  may tag the usage statistics of the designated user with either variation A or variation B. These usage statistics along with the tag may then be provided to servers  206  so that the provider of application  100  may analyze this information and determine how to improve application  100 . Although the set of experiments is described as being conducted in connection with several users, the set of experiments can be conducted in connection with any number of users. 
       FIG. 5  conceptually illustrates electronic system  500  with which any implementations of the subject technology are implemented. Electronic system  500 , for example, can be a desktop computer, a laptop computer, a tablet computer, a server, a phone, a personal digital assistant (PDA), any device that can be used for conducting a set of experiments on an application, or generally any electronic device that transmits signals over a network. Such an electronic system includes various types of computer readable media and interfaces for various other types of computer readable media. Electronic system  500  includes bus  508 , processing unit(s)  512 , system memory  504 , read-only memory (ROM)  510 , permanent storage device  502 , input device interface  514 , output device interface  506 , and network interface  516 , or subsets and variations thereof. 
     Bus  508  collectively represents all system, peripheral, and chipset buses that communicatively connect the numerous internal devices of electronic system  500 . In one or more implementations, bus  508  communicatively connects processing unit(s)  512  with ROM  510 , system memory  504 , and permanent storage device  502 . From these various memory units, processing unit(s)  512  retrieves instructions to execute and data to process in order to execute the processes of the subject disclosure. The processing unit(s) can be a single processor or a multi-core processor in different implementations. 
     ROM  510  stores static data and instructions that are needed by processing unit(s)  512  and other modules of the electronic system. Permanent storage device  502 , on the other hand, is a read-and-write memory device. This device is a non-volatile memory unit that stores instructions and data even when electronic system  500  is off. One or more implementations of the subject disclosure use a mass-storage device (such as a magnetic or optical disk and its corresponding disk drive) as permanent storage device  502 . 
     Other implementations use a removable storage device (such as a floppy disk, flash drive, and its corresponding disk drive) as permanent storage device  502 . Like permanent storage device  502 , system memory  504  is a read-and-write memory device. However, unlike storage device  502 , system memory  504  is a volatile read-and-write memory, such as random access memory. System memory  504  stores any of the instructions and data that processing unit(s)  512  needs at runtime. In one or more implementations, the processes of the subject disclosure are stored in system memory  504 , permanent storage device  502 , and/or ROM  510 . From these various memory units, processing unit(s)  512  retrieves instructions to execute and data to process in order to execute the processes of one or more implementations. 
     Bus  508  also connects to input and output device interfaces  514  and  506 . Input device interface  514  enables a user to communicate information and select commands to the electronic system. Input devices used with input device interface  514  include, for example, alphanumeric keyboards and pointing devices (also called “cursor control devices”). Output device interface  506  enables, for example, the display of images generated by electronic system  500 . Output devices used with output device interface  506  include, for example, printers and display devices, such as a liquid crystal display (LCD), a light emitting diode (LED) display, an organic light emitting diode (OLED) display, a flexible display, a flat panel display, a solid state display, a projector, or any other device for outputting information. One or more implementations may include devices that function as both input and output devices, such as a touchscreen. In these implementations, feedback provided to the user can be any form of sensory feedback, such as visual feedback, auditory feedback, or tactile feedback; and input from the user can be received in any form, including acoustic, speech, or tactile input. 
     Finally, as shown in  FIG. 5 , bus  508  also couples electronic system  500  to a network (not shown) through network interface  516 . In this manner, the computer can be a part of a network of computers (such as a local area network (“LAN”), a wide area network (“WAN”), or an Intranet, or a network of networks, such as the Internet. Any or all components of electronic system  500  can be used in conjunction with the subject disclosure. 
     Many of the above-described features and applications may be implemented as software processes that are specified as a set of instructions recorded on a computer readable storage medium (alternatively referred to as computer-readable media, machine-readable media, or machine-readable storage media). When these instructions are executed by one or more processing unit(s) (e.g., one or more processors, cores of processors, or other processing units), they cause the processing unit(s) to perform the actions indicated in the instructions. Examples of computer readable media include, but are not limited to, RAM, ROM, read-only compact discs (CD-ROM), recordable compact discs (CD-R), rewritable compact discs (CD-RW), read-only digital versatile discs (e.g., DVD-ROM, dual-layer DVD-ROM), a variety of recordable/rewritable DVDs (e.g., DVD-RAM, DVD-RW, DVD+RW, etc.), flash memory (e.g., SD cards, mini-SD cards, micro-SD cards, etc.), magnetic and/or solid state hard drives, ultra density optical discs, any other optical or magnetic media, and floppy disks. In one or more implementations, the computer readable media does not include carrier waves and electronic signals passing wirelessly or over wired connections, or any other ephemeral signals. For example, the computer readable media may be entirely restricted to tangible, physical objects that store information in a form that is readable by a computer. In one or more implementations, the computer readable media is non-transitory computer readable media, computer readable storage media, or non-transitory computer readable storage media. 
     In one or more implementations, a computer program product (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, declarative or procedural languages, and it can be deployed in any form, including as a stand alone program or as a module, component, subroutine, object, or other unit suitable for use in a computing environment. A computer program may, but need not, correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network. 
     While the above discussion primarily refers to microprocessor or multi-core processors that execute software, one or more implementations are performed by one or more integrated circuits, such as application specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs). In one or more implementations, such integrated circuits execute instructions that are stored on the circuit itself. 
     Those of skill in the art would appreciate that the various illustrative blocks, modules, elements, components, methods, and algorithms described herein may be implemented as electronic hardware, computer software, or combinations of both. To illustrate this interchangeability of hardware and software, various illustrative blocks, modules, elements, components, methods, and algorithms have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application. Various components and blocks may be arranged differently (e.g., arranged in a different order, or partitioned in a different way) all without departing from the scope of the subject technology. 
     It is understood that any specific order or hierarchy of blocks in the processes disclosed is an illustration of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of blocks in the processes may be rearranged, or that all illustrated blocks be performed. Any of the blocks may be performed simultaneously. In one or more implementations, multitasking and parallel processing may be advantageous. Moreover, the separation of various system components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the described program components and systems can generally be integrated together in a single software product or packaged into multiple software products. 
     As used in this specification and any claims of this application, the terms “computer”, “server”, “processor”, and “memory” all refer to electronic or other technological devices. These terms exclude people or groups of people. For the purposes of the specification, the terms “display” or “displaying” means displaying on an electronic device. 
     As used herein, the phrase “at least one of” preceding a series of items, with the term “and” or “or” to separate any of the items, modifies the list as a whole, rather than each member of the list (i.e., each item). The phrase “at least one of” does not require selection of at least one of each item listed; rather, the phrase allows a meaning that includes at least one of any one of the items, and/or at least one of any combination of the items, and/or at least one of each of the items. By way of example, the phrases “at least one of A, B, and C” or “at least one of A, B, or C” each refer to only A, only B, or only C; any combination of A, B, and C; and/or at least one of each of A, B, and C. 
     The predicate words “configured to”, “operable to”, and “programmed to” do not imply any particular tangible or intangible modification of a subject, but, rather, are intended to be used interchangeably. In one or more implementations, a processor configured to analyze and control an operation or a component may also mean the processor being programmed to analyze and control the operation or the processor being operable to analyze and control the operation. Likewise, a processor configured to execute code can be construed as a processor programmed to execute code or operable to execute code. 
     A phrase such as “an aspect” does not imply that such aspect is essential to the subject technology or that such aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. An aspect may provide one or more examples of the disclosure. A phrase such as an “aspect” may refer to one or more aspects and vice versa. A phrase such as an “embodiment” does not imply that such embodiment is essential to the subject technology or that such embodiment applies to all configurations of the subject technology. A disclosure relating to an embodiment may apply to all embodiments, or one or more embodiments. An embodiment may provide one or more examples of the disclosure. A phrase such an “embodiment” may refer to one or more embodiments and vice versa. A phrase such as a “configuration” does not imply that such configuration is essential to the subject technology or that such configuration applies to all configurations of the subject technology. A disclosure relating to a configuration may apply to all configurations, or one or more configurations. A configuration may provide one or more examples of the disclosure. A phrase such as a “configuration” may refer to one or more configurations and vice versa. 
     The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described herein as “exemplary” or as an “example” is not necessarily to be construed as preferred or advantageous over other embodiments. Furthermore, to the extent that the term “include,” “have,” or the like is used in the description or the claims, such term is intended to be inclusive in a manner similar to the term “comprise” as “comprise” is interpreted when employed as a transitional word in a claim. 
     All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. No claim element is to be construed under the provisions of 35 U.S.C. §112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.” 
     The previous description is provided to enable any person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but are to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the term “some” refers to one or more. Pronouns in the masculine (e.g., his) include the feminine and neuter gender (e.g., her and its) and vice versa. Headings and subheadings, if any, are used for convenience only and do not limit the subject disclosure.