This disclosure involves personalizing user experiences with electronic content based on application usage data. For example, a user representation model that facilitates content recommendations is iteratively trained with action histories from a content manipulation application. Each iteration involves selecting, from an action history for a particular user, an action sequence including a target action. An initial output is computed in each iteration by applying a probability function to the selected action sequence and a user representation vector for the particular user. The user representation vector is adjusted to maximize an output that is generated by applying the probability function to the action sequence and the user representation vector. This iterative training process generates a user representation model, which includes a set of adjusted user representation vectors, that facilitates content recommendations corresponding to users' usage pattern in the content manipulation application.
Please help me write a proper abstract based on the patent claims. CLAIM: 1. A method for learning, from application usage data, user representations that are usable for personalizing user experiences with electronic content, the method comprising: accessing, by a computing system and from a memory device, training action histories for users of a content manipulation application, wherein each training action history comprises a respective sequence of user actions performed by a respective user with the content manipulation application; accessing, by the computing system and a user representation model, wherein the user representation model includes a probability function and user representation vectors indicating respective software usage patterns for the users; training, by the computing system, the user representation model via iterations, wherein training the user representation model comprises, for each iteration of least some of the iterations: selecting, from a respective training action history for a respective user, respective training data comprising (i) a respective target action, (ii) a respective set of previous actions performed before the respective target action, and (iii) a respective set of subsequent actions performed after the respective target action, computing a respective initial output by applying the probability function to the respective set of previous actions, the respective set of subsequent actions, and a respective user representation vector for the respective user, adjusting the respective user representation vector for the respective user based on the respective initial output being less than a respective maximized output of the probability function, and computing the respective maximized output by applying the probability function to the respective set of previous actions, the respective set of subsequent actions, and the respective user representation vector as adjusted; and outputting a set of adjusted user representation vectors from the trained user representation model, wherein the adjusted user representation vectors optimize the user representation model for predicting target actions in the content manipulation application from sequences of actions in the content manipulation application. 2. The method of claim 1, wherein the user representation model further comprises (i) a weight vector, (ii) an action representation matrix having action vectors representing available actions in the content manipulation application, and (iii) a user representation matrix having the user representation vectors, wherein each sequence of user actions in the training action histories comprises a respective subset of the action vectors, wherein the initial outputs are computed, in the iterations, by applying the probability function to the weight vector, the action representation matrix, and the user representation matrix in addition to the respective set of previous actions, the respective set of subsequent actions, and the respective user representation vector for the respective user, wherein training the user representation model comprises adjusting dimension values in the weight vector, adjusting dimension values of the action vectors used to represent the available actions in the action representation matrix, and adjusting dimension values of the user representation vectors used to represent usage patterns in the user representation matrix, wherein the weight vector, the action representation matrix, and the user representation matrix are adjusted based on at least some initial outputs of the probability function being less than corresponding maximized outputs of the probability function for at least some of the training action histories. 3. The method of claim 2, wherein, for each iteration, the probability function computes a respective probability of the respective target action using a transfer function that combines the respective user representation vector, a respective subset of the action vectors representing the respective set of previous actions and the respective set of subsequent actions, the action vectors from the action representation matrix, and the user representation vectors from the user representation matrix. 4. The method of claim 3, wherein the probability function computes each probability by applying a softmax function to a transfer function output computed with the transfer function, wherein the probability function computes the initial outputs and the maximized outputs from a logarithmic function that is respectively applied to the probabilities. 5. The method of claim 1, further comprising: learning, with the computing system, a projection function that transforms the adjusted user representation vectors into recommendation user representation vectors, respectively, that are usable with a recommendation model for computing recommendation values indicating user preferences for content items accessible via an online content service that is separate from the content manipulation application; accessing, by the computing system, an input user representation vector that is computed from an input action history in the content manipulation application; transforming, with the computing system, the input user representation vector into a transformed user representation vector by applying the projection function to the input user representation vector; and generating, with the computing system, a content recommendation in the online content service by applying the recommendation model to the transformed user representation vector. 6. The method of claim 5, further comprising computing the recommendation user representation vectors, wherein computing each recommendation user representation vector comprises: identifying, based on a respective training viewing history from the online content service, a respective set of content items that has been previously accessed, via the online content service, by a respective user associated with the respective training viewing history; identifying a user-item loss function that relates the respective set of content items to (i) a respective initial recommendation user representation vector of the respective user and (ii) a respective set of item representation vectors representing the respective set of content items; minimizing the user-item loss function by modifying the respective initial recommendation user representation vector into the recommendation user representation vector and adjusting dimension values in the respective set of item representation vectors, wherein minimizing the user-item loss function optimizes the recommendation model, wherein the optimized recommendation model computes, from the recommendation user representation vector and the respective set of item representation vectors with the adjusted dimension values, training recommendation values that are proportional to preferences of the respective user for the respective set of content items. 7. The method of claim 6, wherein learning the projection function comprises minimizing a projection loss function that relates the recommendation user representation vector to a training vector that is computed by applying the projection function to a corresponding one of the user representation vectors from the trained user representation model. 8. The method of claim 6, wherein generating the content recommendation comprises computing, with the optimized recommendation model, output recommendation values from the transformed user representation vector and an item representation vector with adjusted dimension values. 9. A system comprising: a non-transitory computer-readable medium storing training action histories for users of a content manipulation application, wherein the training action histories comprise sequences of user actions performed by users with the content manipulation application; means for selecting, from a training action history for a user, training data comprising a target action and a sequence of user actions including the target action; means for computing an initial output of the target action by applying a probability function to the sequence of user actions and a user representation vector for the user; means for adjusting the user representation vector for the user based on the initial output being less than a maximized output of the probability function; and means for computing the maximized output by applying the probability function to the sequence of user actions and the adjusted user representation vector; and means for transforming an input user representation vector into a transformed user representation vector by applying, to the input user representation vector, a projection function learned from the adjusted user representation vector and a different user representation vector, the different user representation vector based on usage data generated by an online content service that is separate from the content manipulation application; and means for generating, based on the transformed user representation vector, a content recommendation in the online content service. 10. The system of claim 9, further comprising means for training, via iterations, a user representation model usable for computing the input user representation vector, wherein the user representation model includes: a weight vector, an action representation matrix having action vectors representing available actions in the content manipulation application, wherein each sequence of user actions in the training action histories comprises a respective subset of the action vectors, and a user representation matrix having user representation vectors that include the user representation vector, wherein training the user representation model comprises, for each iteration of least some of the iterations, selecting, from a respective training action history for a respective user, a respective target action and a respective sequence of user actions included previous actions performed before the respective target action and subsequent actions performed after the respective target action, computing a respective initial output by applying the probability function to the respective sequence of user actions, a respective user representation vector for the respective user, the weight vector, the action representation matrix, and the user representation matrix, and based on the respective initial output being less than a maximized output of the probability function for the respective sequence of user actions: adjusting dimension values in the weight vector, adjusting dimension values of the action vectors used to represent the available actions in the action representation matrix, and adjusting dimension values of the user representation vectors used to represent usage patterns in the user representation matrix. 11. The system of claim 10, wherein, for each iteration of least some of the iterations, the probability function computes a respective probability of the respective target action using a transfer function that combines the respective user representation vector, a respective subset of the action vectors representing the respective sequence of user actions, the action vectors from the action representation matrix, and the user representation vectors from the user representation matrix. 12. The system of claim 11, wherein the probability function computes each probability by applying a softmax function to a transfer function output computed with the transfer function, wherein the probability function computes the initial outputs and the maximized outputs from a logarithmic function that is respectively applied to the probabilities. 13. The system of claim 10, further comprising computing recommendation user representation vectors that include the different user representation vector, wherein computing each recommendation user representation vector comprises: identifying, based on a respective training viewing history from the online content service, a respective set of content items that has been previously accessed, via the online content service, by a respective user associated with the respective training viewing history; identifying a user-item loss function that relates the respective set of content items to (i) a respective initial recommendation user representation vector of the respective user and (ii) a respective set of item representation vectors representing the respective set of content items; minimizing the user-item loss function by modifying the respective initial recommendation user representation vector into the recommendation user representation vector and adjusting dimension values in the respective set of item representation vectors, wherein minimizing the user-item loss function optimizes a recommendation model that generates recommendation values indicating user preferences for content items accessible via the online content service, wherein the optimized recommendation model computes, from the recommendation user representation vector and the respective set of item representation vectors with the adjusted dimension values, training recommendation values that are proportional to preferences of the respective user for the respective set of content items. 14. The system of claim 13, further comprising means for learning the projection function by minimizing a projection loss function that relates the recommendation user representation vector to a training vector that is computed by applying the projection function to a corresponding one of the user representation vectors from the trained user representation model. 15. The system of claim 13, wherein generating the content recommendation comprises computing, with the optimized recommendation model, output recommendation values from the transformed user representation vector and an item representation vector with adjusted dimension values. 16. A non-transitory computer-readable medium having program code that is stored thereon and that is executable by a processing device for performing operations, the operations comprising: accessing training action histories for users of a content manipulation application, wherein each training action history comprises a respective sequence of user actions performed by a respective user with the content manipulation application; accessing a user representation model, wherein the user representation model includes a probability function and user representation vectors indicating respective software usage patterns for the users; training the user representation model via iterations, wherein training the user representation model comprises, for each iteration of least some of the iterations: selecting, from a respective training action history for a respective user, respective training data comprising (i) a respective target action, (ii) a respective set of previous actions performed before the respective target action, and (iii) a respective set of subsequent actions performed after the respective target action, computing a respective initial output by applying the probability function to the respective set of previous actions, the respective set of subsequent actions, and a respective user representation vector for the respective user, adjusting the respective user representation vector for the respective user based on the respective initial output being less than a respective maximized output of the probability function, and computing the respective maximized output by applying the probability function to the respective set of previous actions, the respective set of subsequent actions, and the respective user representation vector as adjusted; and outputting a set of adjusted user representation vectors from the trained user representation model, wherein the adjusted user representation vectors optimize the user representation model for predicting target actions in the content manipulation application from sequences of actions in the content manipulation application. 17. The non-transitory computer-readable medium of claim 16, wherein the user representation model further comprises (i) a weight vector, (ii) an action representation matrix having action vectors representing available actions in the content manipulation application, and (iii) a user representation matrix having the user representation vectors, wherein each sequence of user actions in the training action histories comprises a respective subset of the action vectors, wherein the initial outputs are computed, in the iterations, by applying the probability function to the weight vector, the action representation matrix, and the user representation matrix in addition to the respective set of previous actions, the respective set of subsequent actions, and the respective user representation vector for the respective user, wherein training the user representation model comprises adjusting dimension values in the weight vector, adjusting dimension values of the action vectors used to represent the available actions in the action representation matrix, and adjusting dimension values of the user representation vectors used to represent usage patterns in the user representation matrix, wherein the weight vector, the action representation matrix, and the user representation matrix are adjusted based on at least some initial outputs of the probability function being less than corresponding maximized outputs of the probability function for at least some of the training action histories. 18. The non-transitory computer-readable medium of claim 17, wherein, for each iteration, the probability function computes a respective probability of the respective target action using a transfer function that combines the respective user representation vector, a respective subset of the action vectors representing the respective set of previous actions and the respective set of subsequent actions, the action vectors from the action representation matrix, and the user representation vectors from the user representation matrix. 19. The non-transitory computer-readable medium of claim 16, the operations further comprising: learning, with the computing system, a projection function that transforms the adjusted user representation vectors into recommendation user representation vectors, respectively, that are usable with a recommendation model for computing recommendation values indicating user preferences for content items accessible via an online content service that is separate from the content manipulation application; accessing, by the computing system, an input user representation vector that is computed from an input action history in the content manipulation application; transforming, with the computing system, the input user representation vector into a transformed user representation vector by applying the projection function to the input user representation vector; and generating, with the computing system, a content recommendation in the online content service by applying the recommendation model to the transformed user representation vector. 20. The non-transitory computer-readable medium of claim 19, the operations further comprising computing the recommendation user representation vectors, wherein computing each recommendation user representation vector comprises: identifying, based on a respective training viewing history from the online content service, a respective set of content items that has been previously accessed, via the online content service, by a respective user associated with the respective training viewing history; identifying a user-item loss function that relates the respective set of content items to (i) a respective initial recommendation user representation vector of the respective user and (ii) a respective set of item representation vectors representing the respective set of content items; minimizing the user-item loss function by modifying the respective initial recommendation user representation vector into the recommendation user representation vector and adjusting dimension values in the respective set of item representation vectors, wherein minimizing the user-item loss function optimizes the recommendation model, wherein the optimized recommendation model computes, from the recommendation user representation vector and the respective set of item representation vectors with the adjusted dimension values, training recommendation values that are proportional to preferences of the respective user for the respective set of content items.