Mathematical Problems in Engineering

Mathematical Problems in Engineering / 2018 / Article

Research Article | Open Access

Volume 2018 |Article ID 1737840 | 10 pages | https://doi.org/10.1155/2018/1737840

Interval Forecasting in Supply Chain with Small Sample

Academic Editor: Rafał Stanisławski
Received31 Jul 2018
Accepted18 Sep 2018
Published01 Oct 2018

Abstract

To deal with the forecasting with small samples in the supply chain, three grey models with fractional order accumulation are presented. Human judgment of future trends is incorporated into the order number of accumulation. The output of the proposed model will provide decision-makers in the supply chain with more forecasting information for short time periods. The results of practical real examples demonstrate that the model provides remarkable prediction performances compared with the traditional forecasting model.

1. Introduction

The supply chain forecasting can be made more accurate when human judgements are incorporated into the forecast system [1]. The performance of purely quantitative forecasting method can be flawed when historical data is limited [2]. In certain cases, the number of available samples is so scarce that providing reliable estimates is a challenging problem [3]. In order to analyze and predict the small samples systems accurately, a large number of studies on supply chain forecasting using grey models and improved grey models have been reported [47]. The GM(1,1) (grey first-order differential equation model) forecasting model is formulated for solving limited time series data [8]. There is no strict hypothesis for the distribution of parent data. However, the reliability and validity of the GM(1,1) have never been discussed. First, without considering other causes when using limited time series data, the forecasting of the GM(1,1) is unreliable and provides insufficient information to a decision-maker. Second, human judgment cannot be incorporated into the forecasting systems. A grey prediction model with fractional-order accumulation is newly proposed and has better performance and more freedom compared with the traditional grey model [9]. Multivariable nonequidistance grey model with fractional order accumulation is discussed [10]. The grey model predictor design is modified by using optimal fractional-order accumulation calculus [11]. The air quality indicators in the Beijing-Tianjin-Hebei region are predicted by the grey prediction model with fractional-order accumulation [12]. Therefore, in This paper, three grey models with fractional-order accumulation are put forward. The output of the proposed model can obtain a general interval. This interval is not the grey number [13]. It will provide more forecasting information for a short time period. Most importantly, human judgment for future trend is incorporated into the order number of accumulation.

The rest of the paper proceeds as follows. Grey single variable forecasting models with fractional order accumulation are presented in Section 2. The multivariable grey model with fractional order accumulation is proposed in Section 3. Interval forecasting method of grey models for supply chain management is discussed in Section 4. Some conclusions are given in the last section.

2. Grey Single Variable Forecasting Models with Fractional Order Accumulation

For the original data sequence , a new sequence can be generated by the fractional order accumulated generating operator (FAGO) as [14]. (1,1) model and grey exponential smoothing are given in the following way.

2.1. Model

Definition 1. is referred to as the original form of the (1,1) model, where It is the traditional GM(1,1) model when . The ordinary least squares estimate sequence of the (1,1) model satisfieswhere

The solution of the whitenization equation for (1,1) is given by

The order inverse accumulated generating operator (IAGO) of is

The procedures of (1,1) can be summarized as follows.

Step 1. For the sequence from [4], 0.7-order accumulation sequence and in (2) are

Step 2. Substituting and into (2), we have the parameters . Then (1,1) can be represented as

Step 3. The 0.7-order accumulated generating operation values can be obtained by employing (4): The 2-order accumulated generating operation values is

The predicted values are , which are listed in Table 1. Mean absolute percentage error () compares the actual values with the forecasted values to evaluate the precision. The use of intelligent methods is a new trend in the grey models [15, 16]. In this paper, particle swarm optimization is adopted to find the optimal order which produces the minimum MAPE. The experiments are conducted in the MATLAB R2015b.


Timeresilience performanceGM(1,1)(1,1)

1176317631763
2237624412384
3276326852740
4298329543002
5321632503211
MAPE2.00.4

The results of Table 1 mean that (1,1) have better performance than the traditional GM(1,1). To investigate the feasibility of the (1,1) model in the supply chain, the following cases are given.

The Supply Chain Performance Resilience Forecasting Example [4]. The periodic resilience performance indicators of case firm are listed in Table 2. By (1,1), respectively, the forecasting values and MAPE of different models are given in Table 3.


TimeRPI 1RPI 2RPI 3RPI 4RPI 5

12386134567467841763
22399187656756472376
33453234545345632763
43645278436337432983
54064376427833453216


RPI 1RPI 2RPI 3RPI 4RPI 5

MAPE of GM(1,1)63132
MAPE of (1,1)4.12.30.41.20.4

In Table 3, the error analysis shows that (1,1) ensure the best fit of the data to achieve strong prediction capability. (1,1) can predict the supply chain resilience of an Indian electronics manufacturer.

The Sales Volume of Printers Forecasting Example [20]. Shih et al used the sales volume of printers from 2002 to 2007 as training data. The volume of 2008 is the testing data. Actual values are listed in Table 4 and the errors of eight models are shown in Table 5. The results show that the forecasting accuracy of the (1,1) is better than traditional GM(1,1).


Year2002200320042005200620072008

Sales volume1047957113844010917051083829981984838822820161


Forecasting techniqueForecasting value for 2008Actual valueMAPE

Moving average91040311.0
Exponential smoothing8541684.1
Quadratic trend64669921.2
Cubic trend66562982016118.8
Non-linear trend8769986.9
ANP830797 1.3
(1,1)8171420.4
GM(1,1)8360181.9

The LCD TV Demand Forecasting Example [19]. Tsaur collected the LCD TV demand data from 2001 to 2006 as shown in Table 6. It was obvious that the collected data are limited time series data, and therefore the possible methods such as GM(1,1) and single exponential smoothing model were used for forecasting. The forecasting results are shown in Table 6. In Table 6, we find that the (1,1) has better forecasting performance of MAPE than the single exponential smoothing model.


YearLCD TV demandsingle exponential modelAR model(1,1)

2001815981
200215015195197
2003393149183423
2004970567505898
20052018108610921903
20064300268225514026
MAPE37.641.110.9

2.2. Grey Exponential Smoothing Model

FAGO is widely used in grey models for its ability to smooth the randomness of original data [9]. Through FAGO, the disorderly data may be converted into regular form. Actually, by using FAGO, the disorderly sequence may be converted into an approximately increased sequence. For example, , the -AGO sequence is The lines of these sequences are illustrated in Figures 1 and 2, respectively. Comparing the two lines, it is clear that the trend of sequence in Figure 2 is more obvious than the sequence in Figure 1.

An irregular and increased sequence can be predicted by using double exponential smoothing (GDES). Then we give the following definition.

Definition 2 (see [21]). For the original time series , -AGO is given in Definition 1. GDES follows the equations where and are the single and double exponential smoothing values for time , respectively. The forecasting form is .

If , GDES is the traditional double exponential smoothing. The process of calculating GDES can be summarized as follows.

Step 1. Set the order number and obtain the -FAGO sequence of according to Definition 1.

Step 2. Calculate the parameters ( and ) by using Definition 2.

Step 3. Compute the predictive value using , where is the out-of-sample size.

Step 4. Transform the prediction value back to the original sequence by means of IAGO [21].

In this paper, the predictive values are calculated by using different s. The that produces a small mean square error for the fitted values and shows an expected future growth is chosen. We assumed that and are equal to the initial historical values.

In this case, the data from [17] is the spare demand of a firm. The accuracy of demand forecast significantly affects the firm‘s sustainability and profitability. To compare the GDES with traditional double exponential smoothing, the smoothing constant of GDES and traditional double exponential smoothing is set to . The predictive values of two models are shown in Table 7.


YearActual demand [17]GDEStraditional double exponential smoothing

2006161616
200733-2
2008794
200922-1
2010443
2011565
MAPE8.562.4

As shown in Table 7, GDES can enhance the accuracy of small data forecasting.

3. The Multivariable Grey Model with Fractional Order Accumulation

The existing multivariable grey models (GMC(1,N)) all used first-order accumulated generating operation sequence [2226]. In this section, the fractional order accumulated generating operation sequence is introduced into the GMC(1,N) model.

Definition 3. It is assumed that is the sequence of system characteristic and ,N) are the sequences of relevant factors. Then is the (1,N) model, where is the order accumulation of , [14]. It is the traditional GMC(1,N) model when . Using ordinary least squares, the parameters of (1,N) model are estimated: where

Set ; when , the convolution integral of the right hand of (12) can also be discretised as where Then the order inverse accumulated generating operator of the predicted value is the same as (5).

For example, the customer perception indicators of engine product are listed in Table 8 from [18]. To obtain the sales volume forecasting value, the engine sales volume is . Energy efficiency, product safety, cost performance, and service promptness are , and , respectively. This case has limited data. Thus we can build (1,5). (1,5) has the smaller MAPE than the (1,5) with the other accumulated order numbers. Thus the results of (1,5) are given in Table 9.


Yearsales volumeenergy efficiencyproduct safetycost performanceservice promptness

2005850.158.2112111
2006972.188.50271.03261.07861.0405
20071078.478.27111.03521.10291.007
20081069.288.08061.05211.06240.9818
20091259.268.19151.08461.02771.0028
20101454.519.08491.09111.07051.1229
20111413.928.79341.04040.99081.0796
20121672.118.90421.06120.97691.0992
20131948.239.39611.12891.02431.1704
20142063.359.9381.22140.97111.3701


Yearsales volumeQuadratic polynomial model [18](1,5)

2005850.15850.15850.15
2006972.18861.7971965.79
20071078.47929.55401055.96
20081069.281058.69181144.18
20091259.261103.40971264.41
20101454.511285.51181399.63
20111413.921525.67921555.71
20121672.111567.08151743.53
20131948.231786.33521934.37
20142063.352095.02472100.82
MAPE8.243.0

By comparing the MAPE in Table 9, the example of demand forecasting for engine products demonstrated the applicability and validity of the (1,5).

Actually, is taken as the supply chain demand. ,N) are the sequences of relevant factors. (1,N) are suitable to predict the supply chain demand, because (1,N) can depict the model more precisely with new degrees of freedom and performances.

4. Interval Forecasting of Grey Models for Supply Chain Management

Fractional derivatives accumulate the whole history of the system in weighted form and it is referred to as the memory effect. As we know, big samples forecasting models depend on statistical laws. In this section, the small samples forecasting models which depend on the memory effect are a new path. For example, in grey forecasting models denotes the weight of as 1. The larger of is, the larger the weight of old data is. The smaller of is, the smaller the weight of old data is. Reducing can reduce the weights of old data, which can put more emphasis on the newer data.

Although the grey models (including (1,1), , and (1,N)) have better forecasting performance, the input data is too limited and the forecasting values are point estimations which supply too limited information for a decision-maker. In this section, in order to obtain a better fitted model with smaller estimated errors and a smaller support forecasting interval, a novel fractional grey modelling mechanism is applied for solving limited time series data using the following steps.

Actually, for many forecasting cases in the supply chain, the accumulated order number often satisfied . If the future trend is similar to the newer data, the setting value of is smaller. If the future trend is similar to the order data, the setting value of is bigger. In the supply chain. for many forecasting cases with limited information, if it is difficult to judge the future trend, the forecasting value must be in a forecasting interval. The upper value and the lower value of forecasting interval can be obtained by different fractional grey models.

For the original data sequence , the forecasting values of (1,1) model (or and (1,N)) are denoted as and the forecasting values of (1,1) model (or and (1,N)) are denoted as For the same point , the smaller of and is set to the lower value of the forecasting interval. The bigger of and is set to the upper value of the forecasting interval. Thus we can obtain a grey forecasting interval. For example, the forecasting values of (1,1) model (or and (1,N)) are and the forecasting values of (1,1) model (or and (1,N)) are Therefore, the grey forecasting interval values are The above method is called the grey interval model (GIM). To investigate the feasibility of GIM in supply chain forecasting, seven cases are listed as follows.

Case 1. The data are from [27]. The data come from the sales volume of semiconductor components in a firm. To compare the proposed model with the other model, the data before November are the training set. The fitting values of different models are given in Table 10.
The predictive results (December) of different models are given in Table 11.
We can clearly see from the results given in Table 10 that (1,1) can obtain higher fitting accuracy. From the results given in Table 11, we can see that GIM can obtain shorter intervals including the actual value. But the simple linear regression derives a wide forecasting interval which provides too little information for the decision-maker.


Monthsales volume(1,1)(1,1)

1103148103148103148
2119066119269124066
3137468139992143842
4155892162736164238
5186370187063186099
6216230212887209924
7249776240225236108
8266829269135265023
9294475299698297046
10334595332004332578
11365988366158372051
MAPE1.42.4


modelsales volumepredictive valuesinterval value

simple linear regression (Xue 2015)414032436402[, ]
GIM414032[, ]

Case 2. The data come from [28]. The data refer to the numbers of end-of-life vehicles in the West Anatolia. Forecasting the return flow of an end-of-life product is important for all decision levels of the reverse supply chain. In this paper, the predictive results of GIM are given in Table 12. The results of interval value can provide guidance to the managers and practitioners of recovery and recycling systems.


Yearnumber of end-of-life vehiclesinterval value

20081977[, 1977]
20092455[, 2567]
20102818[, 2527]
20112266[, 2432]
20122241[, 2369]
20132265[, 2320]

Case 3. The data come from [29]. In recent years, China’s high production of thin film transistor liquid crystal display (TFT-LCD) panels has led to intense competition in this industry, causing its supply to be greater than the actual demand. Under such circumstances, reducing inventory levels and inventory turnover is a critical issue faced by panel manufacturers. The production quantity is maintained at an appropriate balance point considering the total cost. To achieve this balance in production marketing coordination, an accurate short-term demand forecast is essential. Because the demand for TFT-LCD panels is affected tremendously by the global business cycle, whereas the business cycle has substantially changed in recent years, the use of numerous long-term historical observations does not satisfy the needs of the short-term forecasts. Therefore, this study applied data produced by a leading Taiwanese TFT-LCD panel manufacturer to verify the forecasting performance of GIM [29]. In this paper, the predictive results of GIM are given in Table 13. The actual value is in the forecasting interval. It demonstrates that GIM can provide more information with predictive values.


MonthsActual value(1,1)(1,1)interval value

41.7181.7181.718[.718, 1.718]
51.7281.7141.715[.714, 1.715]
61.7141.7351.740[.735, 1.740]
71.7531.7461.741[.741, 1.746]
MAPE 0.60.7
81.7421.7481.729[.729, 1.748]

Case 4. The data come from [30]. They are the return quantity for a third party e-waste firm in Turkey. The predictive results are listed in Table 14.
The predictive results in Table 14 indicate that (1,1) and (1,1) can obtain small fitting errors. By GIM, the obtained forecasting interval indeed includes the actual value. Thus, we can conclude that GIM is effective for limited sample forecasting problems.


TimeActual value(1,1)(1,1)interval value

1536.4536.4536.4[.4, 536.4]
2538.61538.2535.8[.8, 538.2]
3569.35569.6554[, 569.6]
4613612.8565.3[.3, 612.8]
MAPE 0.032.7
5633.32664.6572.6[.6, 664.6]

Case 5. Shih et al. used the sales volume of printers from 2002 to 2007 as the training data. The volume of 2008 is the testing data [20]. Actual values are listed in Table 4 and the results of GIM are shown in Table 15. The results show that the actual value of 2008 is in the forecasting interval. Thus, we can conclude that GIM is effective for the limited sample forecasting problem.


Forecasting techniqueActual valueinterval value

GIM820161[, 963371]

Case 6. Actual values are listed in Table 7 and the results of GIM are shown in Table 16. As shown in Table 16, the results show that the actual demand values are all in the forecasting interval. It also indicates that highly volatile demand can obtain volatile intervals. These results can provide more information for the supply chain manager. Thus, we can conclude that GIM is effective for limited sample forecasting problems.


YearActual demand [17]interval value

2006161616
20073-14[-1,]
2008759[,9]
2009202[,2]
2010434[,4]
2011556[,6]

Case 7 (see [19]). Tsaur collected the LCD TV demand data from 2001 to 2006 as shown in Table 6. The forecasting results are shown in Table 17. In Table 17, we find that the interval of GIM is shorter than that of the fuzzy autoregressive model.


YearLCD TV demandthe proposed modelfuzzy autoregressive model [19]

200181
2002150[,210][,276]
2003393[,476][,532]
2004970[,1024][,969]
20052018[,2156][,2163]
20064300[,4493][,4779]

5. Conclusion

In theory, (1,1), , and (1,N) models are discussed in this paper, respectively. Their application scopes are listed in Table 18. The results show that these models outperform the traditional grey models in the prediction precision.


SituationMethod

(1,1)exponential trend
volatile trend
(1,N)multi-variable limited data

Using traditional grey models, the forecasting values of limited data are point estimations which supply too limited information for a decision-maker. It is easy to arouse suspicion for this kind of point estimations. Thus, a novel interval forecasting method is put forward. From the empirical results, we found that the forecasting capability of the GIM is quite encouraging, but those of the time series models are not. In addition, the interval of GIM is smaller than that of the simple linear regression and fuzzy autoregressive model. In the real world, the environment is uncertain and we can only use a limited amount of data to provide future forecasts for a short time period. In this situation, GIM is more satisfactory than the time series model.

In practice, GIM is summarized in Table 19. This paper contributes to the literature with an interval model for small samples forecasting in supply chain. It significantly improves small sample forecasting due to the interval result carrying more information. This paper demonstrates that grey modelling can be successfully applied to the forecasting problem in supply chain. Moreover, the proposed forecasting system can be used as a strategic tool for forecasting under uncertain conditions with a small amount of recent data.


Situation JudgementMethod

the future trend is similar to the newer data is smaller
the future trend is similar to the order data is bigger
difficult to judge the future trendinterval forecasting

For future research, in order to investigate the feasibility of the novel model in supply chain, it may be used for other real world cases for forecasting and the performances of the methods can be compared.

Data Availability

All the data are from the references in this paper.

Conflicts of Interest

The authors declare no conflicts of interest.

Acknowledgments

The relevant researches carried out in this paper are supported by the National Natural Science Foundation of China (No. 71871084, 71401051, and 71801085). We also acknowledge the Project funded by China Postdoctoral Science Foundation (2018M630562).

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Copyright © 2018 Lifeng Wu and Yan Chen. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


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