194 research outputs found
On a class of inverse quadratic eigenvalue problem
AbstractIn this paper, we first give the representation of the general solution of the following inverse monic quadratic eigenvalue problem (IMQEP): given matrices Λ=diag{λ1,…,λp}∈Cp×p, λi≠λj for i≠j, i,j=1,…,p, X=[x1,…,xp]∈Cn×p, rank(X)=p, and both Λ and X are closed under complex conjugation in the sense that λ2j=λ̄2j−1∈C, x2j=x̄2j−1∈Cn for j=1,…,l, and λk∈R, xk∈Rn for k=2l+1,…,p, find real-valued symmetric matrices D and K such that XΛ2+DXΛ+KX=0. Then we consider a best approximation problem: given D̃,K̃∈Rn×n, find (Dˆ,Kˆ)∈SDK such that ‖(Dˆ,Kˆ)−(D̃,K̃)‖W=min(D,K)∈SDK‖(D,K)−(D̃,K̃)‖W, where ‖⋅‖W is a weighted Frobenius norm and SDK is the solution set of IMQEP. We show that the best approximation solution (Dˆ,Kˆ) is unique and derive an explicit formula for it
Solutions to an inverse monic quadratic eigenvalue problem
AbstractGiven n+1 pairs of complex numbers and vectors (closed under complex conjugation), the inverse quadratic eigenvalue problem is to construct real symmetric or anti-symmetric matrix C and real symmetric matrix K of size n×n so that the quadratic pencil Q(λ)=λ2In+λC+K has the given n+1 pairs as eigenpairs. Necessary and sufficient conditions under which this quadratic inverse eigenvalue problem is solvable are obtained. Numerical algorithms for solving the problem are developed. Numerical examples illustrating these solutions are presented
An Inverse Quadratic Eigenvalue Problem for Damped Structural Systems
We first give the representation of the general solution of the following inverse quadratic eigenvalue problem (IQEP): given Λ=diag{λ1,…,λp}∈Cp×p , X=[x1,…,xp]∈Cn×p, and both Λ and X are closed under complex conjugation in the sense that λ2j=λ¯2j−1∈C, x2j=x¯2j−1∈Cn for j=1,…,l, and λk∈R, xk∈Rn for k=2l+1,…, p, find real-valued symmetric (2r+1)-diagonal matrices M, D and K such that MXΛ2+DXΛ+KX=0. We then consider an optimal approximation problem: given real-valued symmetric (2r+1)-diagonal matrices Ma,Da,Ka∈Rn×n, find (M^,D^,K^)∈SE such that ‖M^−Ma‖2+‖D^−Da‖2+‖K^−Ka‖2=infâ¡(M,D,K)∈SE(‖M−Ma‖2+‖D−Da‖2+‖K−Ka‖2), where SE is the solution set of IQEP. We show that the optimal approximation solution (M^,D^,K^) is unique and derive an explicit formula for it
Stiffness matrix modification with vibration test data by displacement feedback technique
A no spill-over method is developed which uses measured normal modes and natural frequencies to adjust a structural dynamics model in light of displacement feedback technique. By the method, the required displacement feedback gain matrix is determined, and thus the updated stiffness matrix which satisfies the characteristic equation is found in the Frobenius norm sense and the large number of unmeasured high-order modal data of the original model is preserved. The method directly identifies, without iteration, and the solution of this problem is of a compact expression. The numerical example shows that the modal measured data are better incorporated into the updated model
Nesterov smoothing for sampling without smoothness
We study the problem of sampling from a target distribution in
whose potential is not smooth. Compared with the sampling problem with smooth
potentials, this problem is much less well-understood due to the lack of
smoothness. In this paper, we propose a novel sampling algorithm for a class of
non-smooth potentials by first approximating them by smooth potentials using a
technique that is akin to Nesterov smoothing. We then utilize sampling
algorithms on the smooth potentials to generate approximate samples from the
original non-smooth potentials. We select an appropriate smoothing intensity to
ensure that the distance between the smoothed and un-smoothed distributions is
minimal, thereby guaranteeing the algorithm's accuracy. Hence we obtain
non-asymptotic convergence results based on existing analysis of smooth
sampling. We verify our convergence result on a synthetic example and apply our
method to improve the worst-case performance of Bayesian inference on a
real-world example
Where to Go Next for Recommender Systems? ID- vs. Modality-based Recommender Models Revisited
Recommendation models that utilize unique identities (IDs) to represent
distinct users and items have been state-of-the-art (SOTA) and dominated the
recommender systems (RS) literature for over a decade. Meanwhile, the
pre-trained modality encoders, such as BERT and ViT, have become increasingly
powerful in modeling the raw modality features of an item, such as text and
images. Given this, a natural question arises: can a purely modality-based
recommendation model (MoRec) outperforms or matches a pure ID-based model
(IDRec) by replacing the itemID embedding with a SOTA modality encoder? In
fact, this question was answered ten years ago when IDRec beats MoRec by a
strong margin in both recommendation accuracy and efficiency. We aim to revisit
this `old' question and systematically study MoRec from several aspects.
Specifically, we study several sub-questions: (i) which recommendation
paradigm, MoRec or IDRec, performs better in practical scenarios, especially in
the general setting and warm item scenarios where IDRec has a strong advantage?
does this hold for items with different modality features? (ii) can the latest
technical advances from other communities (i.e., natural language processing
and computer vision) translate into accuracy improvement for MoRec? (iii) how
to effectively utilize item modality representation, can we use it directly or
do we have to adjust it with new data? (iv) are there some key challenges for
MoRec to be solved in practical applications? To answer them, we conduct
rigorous experiments for item recommendations with two popular modalities,
i.e., text and vision. We provide the first empirical evidence that MoRec is
already comparable to its IDRec counterpart with an expensive end-to-end
training method, even for warm item recommendation. Our results potentially
imply that the dominance of IDRec in the RS field may be greatly challenged in
the future
FMMRec: Fairness-aware Multimodal Recommendation
Recently, multimodal recommendations have gained increasing attention for
effectively addressing the data sparsity problem by incorporating
modality-based representations. Although multimodal recommendations excel in
accuracy, the introduction of different modalities (e.g., images, text, and
audio) may expose more users' sensitive information (e.g., gender and age) to
recommender systems, resulting in potentially more serious unfairness issues.
Despite many efforts on fairness, existing fairness-aware methods are either
incompatible with multimodal scenarios, or lead to suboptimal fairness
performance due to neglecting sensitive information of multimodal content. To
achieve counterfactual fairness in multimodal recommendations, we propose a
novel fairness-aware multimodal recommendation approach (dubbed as FMMRec) to
disentangle the sensitive and non-sensitive information from modal
representations and leverage the disentangled modal representations to guide
fairer representation learning. Specifically, we first disentangle biased and
filtered modal representations by maximizing and minimizing their sensitive
attribute prediction ability respectively. With the disentangled modal
representations, we mine the modality-based unfair and fair (corresponding to
biased and filtered) user-user structures for enhancing explicit user
representation with the biased and filtered neighbors from the corresponding
structures, followed by adversarially filtering out sensitive information.
Experiments on two real-world public datasets demonstrate the superiority of
our FMMRec relative to the state-of-the-art baselines. Our source code is
available at https://anonymous.4open.science/r/FMMRec
HeteFedRec: Federated Recommender Systems with Model Heterogeneity
Owing to the nature of privacy protection, federated recommender systems
(FedRecs) have garnered increasing interest in the realm of on-device
recommender systems. However, most existing FedRecs only allow participating
clients to collaboratively train a recommendation model of the same public
parameter size. Training a model of the same size for all clients can lead to
suboptimal performance since clients possess varying resources. For example,
clients with limited training data may prefer to train a smaller recommendation
model to avoid excessive data consumption, while clients with sufficient data
would benefit from a larger model to achieve higher recommendation accuracy. To
address the above challenge, this paper introduces HeteFedRec, a novel FedRec
framework that enables the assignment of personalized model sizes to
participants. In HeteFedRec, we present a heterogeneous recommendation model
aggregation strategy, including a unified dual-task learning mechanism and a
dimensional decorrelation regularization, to allow knowledge aggregation among
recommender models of different sizes. Additionally, a relation-based ensemble
knowledge distillation method is proposed to effectively distil knowledge from
heterogeneous item embeddings. Extensive experiments conducted on three
real-world recommendation datasets demonstrate the effectiveness and efficiency
of HeteFedRec in training federated recommender systems under heterogeneous
settings
- …