Hybrid Parallel Bessel KAN Model: a Kolmogorov Arnold Network: integrated framework for developing a novel architecture to reconstruct the fused-basis approach via a parameter free quadratic interaction
Organizations: Department of Applied Sciences, Tezpur University, Napaam, Tezpur, 784028, Assam, India. · Department of ICT, Pandit Deendayal Energy University, Raysan, Gandhinagar, 382007, Gujarat, India.
The Kolmogorov-Arnold Network (KAN) challenges traditional MLPs by placing learnable activation functions on network edges. However, scaling KANs to spatial data exposes limitations in default B-Splines. While hybrid architectures mix multiple basis families on a single edge to resolve this, monolithic superposition causes geometric overlap, parameter explosion, and severe numerical ill-conditioning (κ(G)≈1016).To overcome this, we propose Parallel BesselKAN, which isolates B-Spline and low-order Bessel branches into parallel processing pipelines integrated via a parameter-free quadratic interaction. This decoupled architecture acts as an efficient internal ensemble, bypassing monolithic stability bottlenecks. It compresses the parameter footprint by 35% while achieving 97.99% accuracy on MNIST. Although standard MLPs retain a hardware speed advantage for pure vision tasks, Parallel BesselKAN provides a robust, parameter-efficient framework stabilizing mixed-basis networks and paving the way for scalable spatial adaptations like Convolutional KANs.
Figures & tables
Figure 1: Difference between MLP and KAN. Figure adapted from Liu et al. ( Liu et al., 2025 ) under a Creative Commons Attribution 4.0 International License.
Config
κ(Θ)
κ(G)
Rank( Θ )
Rank( G )
Spline only (n=5)
5.50×100
3.02×101
5/5
5/5
Bessel only ( ν=0 – 3 )
2.89×102
8.39×104
4/4
4/4
Hybrid ( s=5,b=4 )
1.46×107
2.13×1014
9/9
9/9
Hybrid ( s=5,b=6 )
1.73×108
3.30×1016
11/11
10/11
Bessel horror ( ν=0 – 7 )
6.09×107
3.67×1015
8/8
7/8
Table 1: Empirical Conditioning and Effective Rank Across Basis Configurations
Figure 2: Spectral characterization and approximation bounds of the hybrid architecture 1: ( a ) Gram matrix condition numbers scale exponentially in hybrid configurations. ( b ) The hybrid model collapses reconstruction RMSE on complex oscillatory targets like sin(5x) .
Figure 3: Spectral characterization and approximation bounds of the hybrid architecture 2: ( c ) The symmetric geometric overlap between the B-spline partition and low-order Bessel functions over [−1,1] drives the primary near-null space.
Figure 4: Expressive capacity versus numerical stability trade-off. Expanding the Bessel truncation order q beyond q=2 yields negligible improvement in mean reconstruction error (RMSE) while causing the design matrix condition number κ(Θ) to grow exponentially, eventually exceeding double-precision limits.
Dataset
Samples (train / test)
Input
Dim.
Classes
Iris
120 / 30
4 tabular features
4
3
MNIST
60,000 / 10,000
28×28 grayscale, flattened
784
10
Fashion-MNIST
60,000 / 10,000
28×28 grayscale, flattened
784
10
CIFAR-10
50,000 / 10,000
32×32×3 RGB, flattened (C,H,W)
3072
10
Table 2: Classification benchmarks. Iris uses a random train/test split of its 150 samples.
Figure 5: Basis functions of the two parametric paths. (a) The five cubic B-spline basis functions on [−1,1] with knot vector (−1,−1,−1,−1,0,1,1,1,1) , evaluated for u∈[−1,1) (at exactly u=1 the implemented basis is zero; Section 6.2 ). (b) The Bessel functions J0 – J3 used in the Bessel path, shown for z∈[−10,10] .
Dataset
Model
Epochs
LR
Batch
Mixing
Seeds
Iris
BesselKAN
60
3×10−3
32
no
5
MNIST
BesselKAN
25
3×10−3
64
no
5
Fashion-MNIST
BesselKAN
35
3×10−3
64
yes
5
CIFAR-10
BesselKAN
25
3×10−3
64
no
5
MNIST / F-MNIST
MLP
25 / 35
10−3
64
–
5
MNIST
Parallel fusion
25
10−3
64
no
1
Table 3: Training configuration. All runs use AdamW (weight decay 10−4 ), gradient-norm clipping at 1.0 and a cosine schedule.
Dataset
Model
Params
Accuracy
Epochs
Time (s)
MNIST
BesselKAN (ours)
516,640
97.53±0.07
25
40.3
MNIST
MLP (param-matched)
516,760
98.55±0.03
25
14.8
MNIST
EfficientKAN Ta (2025)
–
≈97.0
25
–
MNIST
BSRBF-KAN Ta (2025)
–
97.59
25
–
MNIST
FC-KAN (DoG+BS) Ta et al. (2026)
–
97.91
25
–
Fashion-MNIST
BesselKAN + mixing (ours)
516,714
89.34±0.30
35
40.7
Table 4: Test accuracy (%). “Time” is seconds per epoch on the MPS GPU. Literature values were quoted, not re-run.
Figure 6: Test accuracy of the hybrid KAN and the parameter-matched MLP on MNIST and Fashion-MNIST (mean ± standard deviation over five seeds); dashed lines mark the accuracies reported for BSRBF-KAN and FC-KAN. Note the truncated vertical axes.
Configuration
Params
Accuracy (%)
Spline-only ( P=0 )
360
86.0±6.4
Hybrid, P=2
520
84.7±6.5
Hybrid, P=4
680
80.7±6.4
Hybrid, P=6
840
84.7±3.8
Hybrid, P=4 , mixing
691
82.0±6.1
Single-spline request, P=6
784
85.3±6.5
Table 5: Iris ablation (60 epochs, five seeds).
Target
Spline (5)
Bessel (4)
Hybrid (5+4)
sin(5x)
0.3632
0.3535
0.0568
J0(3x)
0.0124
0.0601
0.0006
J1(5x)+J2(3x)
0.1304
0.1322
0.0163
x2
0.0447
0.0066
0.0000
∣x∣
0.0532
0.0669
0.0107
1[x>0]
0.1926
0.1861
0.1504
Table 6: In-sample least-squares fit error (RMSE) on the 500 points.
Figure 7: Learned first-layer edge functions. Left: four shape templates ( k -means, k=4 ) of the standardized edge functions ϕ^(u) over u∈[−1.5,1.5] . Right: share of each template among active edge functions on MNIST and Fashion-MNIST.
Figure 8: Contribution of the spline and Bessel branches of the last layer on MNIST. Left: mean absolute (L1) magnitude per digit class. Right: spline-to-Bessel magnitude ratio per class; colours mark the digit groups (1, 4, 7) and (0, 6, 8).
Kolmogorov-Arnold Networks (KANs) are a recent neural network architecture offering an alternative to Multilayer Perceptrons (MLPs) with improved explainability and expressibility. However, KANs are significantly slower than MLPs due to the recursive nature of B-spline function computations, limiting their application. This work addresses these issues by proposing a novel base-spline Linear-Time B-splines Kolmogorov-Arnold Network (LTBs-KAN) with linear complexity. Unlike previous methods that rely on the Boor-Mansfield-Cox spline algorithm or other computationally intensive mathematical functions, our approach significantly reduces the computational burden. Additionally, we further reduce model's parameter through product-of-sums matrix factorization in the forward pass without sacrificing performance. Experiments on MNIST, Fashion-MNIST and CIFAR-10 demonstrate that LTBs-KAN achieves good time complexity and parameter reduction, when used as building architectural blocks, compared to other KAN implementations.
Eduardo Said Merin-Martinez, Andres Mendez-Vazquez, Eduardo Rodriguez-Tello
Cinvestav, Unidad Guadalajara · Av. del Bosque 1145, El Bajio · Zapopan, Jalisco, 45017, Mexico +3
Algorithmic speedup of training common neural architectures is made difficult by the lack of structure guaranteed by the function compositions inherent to such networks. In contrast to multilayer perceptrons (MLPs), Kolmogorov-Arnold networks (KANs) provide more structure by expanding learned activations in a specified basis. This paper exploits this structure to develop practical algorithms and theoretical insights, yielding training speedup via multilevel training for KANs. To do so, we first establish an equivalence between KANs with spline basis functions and multichannel MLPs with power ReLU activations through a linear change of basis. We then analyze how this change of basis affects the geometry of gradient-based optimization with respect to spline knots. The KANs change-of-basis motivates a multilevel training approach, where we train a sequence of KANs naturally defined through a uniform refinement of spline knots with analytic geometric interpolation operators between models. The interpolation scheme enables a ``properly nested hierarchy'' of architectures, ensuring that interpolation to a fine model preserves the progress made on coarse models, while the compact support of spline basis functions ensures complementary optimization on subsequent levels. Numerical experiments demonstrate that our multilevel training approach can achieve orders of magnitude improvement in accuracy over conventional methods to train comparable KANs or MLPs, particularly for physics informed neural networks. Finally, this work demonstrates how principled design of neural networks can lead to exploitable structure, and in this case, multilevel algorithms that can dramatically improve training performance.
Ben S. Southworth, Jonas A. Actor, Graham Harper +1
Theoretical Division, Los Alamos National Laboratory, USA. · Center for Computing Research, Sandia National Laboratories, USA.
Multi-Layer Perceptrons (MLPs) rely on pre-defined, fixed activation functions, imposing a static inductive bias that forces the network to approximate complex topologies solely through increased depth and width. Kolmogorov-Arnold Networks (KANs) address this limitation through edge-centric learnable functions, yet their formulation suffers from quadratic parameter scaling and architectural rigidity that hinders the effective integration of standard regularization techniques. This paper introduces the DualFlexKAN (DFKAN), a flexible architecture featuring a dual-stage mechanism that independently controls pre-linear input transformations and post-linear output activations. This decoupling enables hybrid networks that optimize the trade-off between expressiveness and computational cost. Unlike standard formulations, DFKAN supports diverse basis function families, including orthogonal polynomials, B-splines, and radial basis functions, integrated with configurable regularization strategies that stabilize training dynamics. Comprehensive evaluations across regression benchmarks, physics-informed tasks, and function approximation demonstrate that DFKAN outperforms both MLPs and conventional KANs in accuracy, convergence speed, and gradient fidelity. The proposed hybrid configurations achieve superior performance with one to two orders of magnitude fewer parameters than standard KANs, effectively mitigating the parameter explosion problem while preserving KAN-style expressiveness. DFKAN provides a principled, scalable framework for incorporating adaptive non-linearities, proving particularly advantageous for data-efficient learning and interpretable function discovery in scientific applications.
Andrés Ortiz, Nicolás J. Gallego-Molina, Carmen Jiménez-Mesa +2
Department of Communications Engineering University of Malaga Malaga, Spain · DaSCI Andalusian Institute of Data Science and Computational Intelligence University of Granada Granada, Spain · Department of signal Theory, Communications and Telematics University of Granada Granada, Spain