By comparing the local optimal values found by 
each particle through circular iterations, when the 
number of iterations reaches the maximum, the global 
optimal parameter taking value 𝐺
_
(
𝑖,3
)
 is 
determined, the optimal parameter taking value of 
[
𝛾, 𝜎
]
 for model training fitting is namely obtained. 
  Step 3: The second optimization determines 
the optimal value of [p, a] 
In the second PSO optimization, except for changing 
the maximum number of iterations to 300 (determined 
by the results of several experiments), the 
initialization settings of the remaining parameters are 
consistent with those of the first optimization. The 
maximum value of the hybrid weight coefficient 𝑎 is 
also set to 1 and the minimum value to 0. The 
polynomial kernel order 𝑝 is taken in the range 
[
2,8
]
. 
The values of 𝑝 and 𝑎 respectively refer to the 
flight velocity and current position of each particle in 
the particle swarm, the global optimal parameter 
values of 
[
𝛾, 𝜎
]
 obtained from the first optimization 
are substituted into the new adaptation function 
constructed based on the hybrid kernel model, and the 
RSME between the fitting value and real value of the 
model training output is also taken as the adaptation 
value. The value of 𝑝, 𝑎 and the new adaptation value 
are stored in the 3-dimensional local vector 
𝑃
_
(
𝑀,3
)
.
 
𝑃
_
[𝑖,1] represents  the 𝑝 value  of 
the 𝑖th particle, 𝑃
_
[
𝑖,2
]
represents the 𝑎 value  of 
the particle. 𝑃
_
[𝑖,3]  represents the optimal 
adaptation value of that particle under the current two 
attributes and the two attributes obtained by the first 
optimization. 
Consistent with the first optimization, the local 
optimal values found by each particle are compared 
through circular iterations, when the number of 
iterations reaches the maximum, the global optimal 
parameter taking value 𝐺
_
(
𝑖,3
)
 can  be 
determined, that is the values of 
[
𝑝, 𝑎
]
 are determined. 
Finally, after all the optimal parameters for the 
hybrid kernel model fitting and training are 
determined by two PSO optimizations, the combined 
values of the two groups of parameters are substituted 
into the hybrid kernel model to obtain the training 
model for user viewing prediction. 
3  EXPERIMENTS 
3.1  Experimental Settings 
3.1.1  Evaluation Metrics 
In this paper, we utilize  two evaluation metrics, Root 
Mean Squared Error 𝑅𝑀𝑆𝐸  and coefficient of 
determination 𝑅
 to objectively evaluate the model’s 
ratings fitting and prediction effects. The evaluation 
metrics are specifically defined as: 
𝑅𝑀𝑆𝐸 =
∑ (
𝑦
−𝑦
)
,                 (4) 
𝑅
=1−
∑ (
)
∑
(
)
,                       (5) 
where 𝑛 denotes the number of input training samples, 
𝑦
 represents the actual output sample value of the 
training, 𝑦
 is the output predicted value obtained by 
the trained model. In general, the closer the value of 
𝑅𝑀𝑆𝐸 is to 0, the better the model is indicated. 𝑦 
represents the average of the actual output sample 
value. The closer the value of 𝑅
 is to 1, the better the 
overall performance of the model. 
3.1.2  Project Settings 
User behaviors are reflected by time, hence we study 
the variation of users viewing over time and user 
viewing emotion to build a training model. Our paper 
proposes a two-dimensional model fitting and training 
based on Time-Series to the series of sentiment values 
of user comments. Afterward, the sentiment value of 
the comments in the following days is predicted based 
on the obtained two-dimensional model. Then the 
predicted sentiment values are substituted into the 
model trained by fitting the three-dimensional viewing 
data which is based on time and comment sentiment 
to predict the viewing values of these days. 
In addition, there is a certain short-term regularity 
in sentiment values of user comments and variation of 
audience ratings during a week interval (Wang, 2014). 
Therefore, we perform model adaptive iterative 
prediction experiments with a sliding window step of 
7 days. With the adaptive method, the corresponding 
model parameters are obtained based on different 
input data, which can effectively improve the fitting 
and prediction performance of the model. 
3.2  Our Model Experiment Results 
The comment sentiment series from the 1st day to 7th 
day are trained and optimized to build a two-
dimensional fitting model to predict the value of 
comment sentiment on the 8th day as an example. The 
optimal combination of parameters of the model is 
obtained by the PSO algorithm twice. 𝛾 =
49.8176224758775 ,  𝜎
= 0.984616850043333 , 
𝑝 =6 ,  𝑎 = 0.774411848246410 . The model 
corresponds to a two-dimensional fitted curve chart of 
the output, which is shown in Fig. 2.