Background technology
Utilize FUZZY SET APPROACH TO ENVIRONMENTAL to carry out Fuzzy Information Granulation to time series and mainly be divided into two steps: discretize and obfuscation.The discretize fundamental purpose is that time series is divided into to some subsequences, and the size of each subsequence is called window; Obfuscation is that the window that discretize is produced carries out obfuscation, generates the timing ambiguity information.The new time series now generated is called the granulation time series.Predict and can obtain the high layer information that former time series can not directly be obtained for the granulation time series.
The process of discretize and obfuscation is called Fuzzy Information Granulation, is designated as the f-granulation.The key of f-granulation is obfuscation, and obfuscation refers to subsequence preset time
on set up an obscure particle
, determine one and can rationally describe
fuzzy set
(with
fuzzy set for domain).Determined
also just determined fuzzy example
, that is:
The process of obfuscation is exactly to determine function
process,
it is fuzzy concept
subordinate function,
.Usually, at first determine the citation form of concept during granulation, then determine concrete subordinate function
.The citation form of obscure particle comprises: triangle, trapezoidal, gaussian-shape, parabolic type etc.Wherein, this patent is mainly for trapezoidal obscure particle, and the subordinate function of trapezoidal obscure particle is:
At present, granulating method commonly used comprises: the Information Granulating method that W.Pedrycz proposes and dirt is non-, Dong Keqiang is to the improvement of the method.
The obscure particle of the Information Granulating method that W.Pedrycz proposes for setting up
basic thought be:
(1) obscure particle can reasonably represent raw data, maximizes
;
(2) obscure particle will have certain singularity, namely minimizes fuzzy set
support, minimize
, wherein
with
it is respectively fuzzy set
the support border.
Obtain following majorized function by above basic thought:
The target of granulation is to make function
obtain maximal value.For given time series granulation window
, the fuzzy granulation algorithm concrete steps of W.Pedrycz are:
Step 1, determine the core of trapezoidal fuzzy set
,
.Will
by the sequence of ascending order, the time series that might as well establish after sequence is still
, when N is even number,
,
; When N is odd number,
.
Step 2, determine that trapezoidal fuzzy set supports lower bound
.Adopt the method for data traversal to calculate
, make
get peaked data value and be the support lower bound
, that is: make function
get peaked
for
the support lower bound, wherein
for
degree of membership.
Step 3, determine that trapezoidal fuzzy set supports the upper bound
.Adopt the method for data traversal to calculate
, make
get peaked data value and be the support upper bound
, that is: make function
get peaked
for
the support lower bound, wherein
for
degree of membership.
Through above-mentioned steps, can determine 4 parameters of trapezoidal fuzzy message particle:
.
Can carry out the granulation operation to any one time series by the W.Pedrycz method; yet the support less of the fuzzy set that the method obtains; be embodied in too much data message and lose, make set up particle lose the alternative meaning to raw data.The reason that causes loss of data is not consider that particle supports the negative effect of data in addition to particle integral body, the degree of membership of the data beyond particle supports is 0, for this situation, dirt is non-, Dong Keqiang improves the method, makes the subordinate function of original trapezoidal fuzzy set into following form:
Improved fuzzy granulation algorithm concrete steps are:
Step 1, determine the core of trapezoidal fuzzy set
,
.Will
by the sequence of ascending order, the time series that might as well establish after sequence is still
, when N is even number,
,
; When N is odd number,
.Write down
with
, wherein
,
.
Step 2, determine that trapezoidal fuzzy set supports lower bound
.Computing method are:
.
Step 3, determine that trapezoidal fuzzy set supports the upper bound
.Computing method are:
.
The method has enlarged the supporting degree to time series data than the W.Pedrycz method; improved the accommodation of degree of membership; in the time series Fuzzy Information Granulation, use at present comparatively general; yet the method is the same with the W.Pedrycz method; definite support upper bound and support lower bound can not comprise all data in window fully, can not guarantee:
An important evaluating standard of time series trend prediction is whether the scope of prediction can comprise following measurement data fully, obviously, adopts at present existing Fuzzy Information Granulation method to carry out trend prediction to time series and can not meet preferably this standard.
The time series trend prediction has been brought into play vital role in numerous industry fields, for example, in the mine safety field, carry out the granulation trend prediction to take the gas density discrete data that per minute gathers as interval, the gas density interval of predict future after 1 hour, judge whether the safety problems such as gas explosion, coal and Gas Outburst that there will be gas density to transfinite and shine; At medicine and hygiene fields, the time series data of patient's cardiogram (ECG) is carried out to trend prediction, the ecg wave form interval in predict future 5 minutes, for severe case's Real-Time Monitoring, patients with coronary heart disease health prevent etc. plays an important role.
Summary of the invention
In order to overcome the shortcoming of above-mentioned prior art, the invention provides a kind of Fuzzy Information Granulation method towards the time series trend prediction, the definite support bound of the method can comprise the discrete data under existing time series window fully.
The present invention realizes with following technical scheme: a kind of Fuzzy Information Granulation method towards the time series trend prediction, a given time series window
, concrete steps are as follows:
Step 1, determine the core of trapezoidal fuzzy set
,
, computing formula is:
Step 2, to the time series window
carry out interpolation, form new time series window
; Will
by the sequence of ascending order, the time series that might as well establish after sequence is still
.
Step 3, determine that trapezoidal fuzzy set supports lower bound
; At the new time series data collection built
the method of middle employing data traversal is calculated
, make
get peaked data value and be the support lower bound
, that is: make function
get peaked
for
the support lower bound, wherein
for
degree of membership.
Step 4, determine that trapezoidal fuzzy set supports the upper bound
; At the new time series data collection built
the method of middle employing data traversal is calculated
, make
get peaked data value and be the support upper bound
, that is: make function
get peaked
for
the support lower bound, wherein
for
degree of membership.
The invention has the beneficial effects as follows: this method is in conjunction with concrete time series application scenarios; the high layer information grain that the Fuzzy Information Granulation trapezoid model towards the time series trend prediction proposed is sought the generation of ginseng method can comprise the sequential discrete data in the bottom-up information grain fully; support preferably the unknown data that discrete data is outer; coordinate existing Forecasting Methodology; can significantly improve the time series trend prediction effect, there is higher realistic meaning and practical value.
Embodiment
For making purpose of the present invention, technical method and advantage clearer, the present invention is described in further detail below in conjunction with the accompanying drawings and the specific embodiments.
As shown in Figure 1, a kind of given time series window of Fuzzy Information Granulation method towards the time series trend prediction
, the Fuzzy Information Granulation trapezoid model towards the time series trend prediction of the present invention is sought ginseng method tool
Body comprises the steps:
Step 1, determine the core of trapezoidal fuzzy set
,
.Computing formula is:
Time series data in practical application is discrete value, the core that its maximal value and minimum value are trapezoidal fuzzy set, and
, can guarantee that actual acquisition sample data in existing time series window is all on fuzzy granulation border
with
between (
).
Step 2, to the time series window
carry out interpolation, form new time series window
.Will
by the sequence of ascending order, the time series that might as well establish after sequence is still
.
In practical application, adopt the fitting of a polynomial interpolation method.Fitting of a polynomial interpolation method commonly used has 4 kinds, is respectively: closest approach, linearity, batten and cube method of interpolation.Adopt spline method relatively evenly the time if the time window size is less and data distribute.
Step 3, determine that trapezoidal fuzzy set supports lower bound
.At the new time series data collection built
the method of middle employing data traversal is calculated
, make
get peaked data value and be the support lower bound
, that is: make function
get peaked
for
the support lower bound, wherein
for
degree of membership.
Step 4, determine that trapezoidal fuzzy set supports the upper bound
.At the new time series data collection built
the method of middle employing data traversal is calculated
, make
get peaked data value and be the support upper bound
, that is: make function
get peaked
for
the support lower bound, wherein
for
degree of membership.
As shown in Figure 2, the scope of the functional value that trapezoidal left and right hypotenuse is corresponding is between [0,1], shows that the numerical value mapping relations are fuzzy; The functional value perseverance of trapezoidal upper edge is 1, shows that the numerical value mapping relations determine.For the time series window
, its value is the concrete actual value gathered, so its FUZZY MAPPING relation should perseverance be 1, i.e. determinacy mapping.To the time series window
carry out difference, form new time series
, the data of two seasonal effect in time series difference sets are the data that newly increase, and these data are the fitting data to original time series, and data have inaccuracy, so the membership function of these data should be between [0,1].Trapezoidal each angle is respectively m, n, a, b in the mapping of transverse axis.
Superiority with an example explanation this method with respect to classic method, for a data set X={141.77,142.72,141.81; 140.00,139.57,139.95,137.39; 135.24,135.30,137.49,136.26; 138.61,138.83,139.72,142.18; 140.77,141.24,140.33,140.64; 138.34} it carries out granulation the Information Granulating method that adopts W.Pedrycz to propose, the particle obtained is respectively:
a?=?137.3900
m?=?139.7200
n?=?139.9500
b?=?140.3300
Specifically as shown in Figure 3.
Adopt the granulating method of the non-proposition of dirt to carry out granulation to it, the particle obtained is respectively:
a?=?135.6300
m?=?139.7200
n?=?139.9500
b?=?142.3320
Specifically as shown in Figure 4.
By Fig. 3 and Fig. 4, can be found out, the data after existing two kinds of granulating method granulations can not comprise existing time series data fully, can not guarantee
An important evaluating standard of time series trend prediction is whether the scope of prediction can comprise following measurement data fully, obviously, adopts at present existing Fuzzy Information Granulation method to carry out trend prediction to time series and can not meet preferably this standard.
It carries out granulation the Information Granulating method that adopts patent of the present invention to propose, and the particle obtained is respectively:
a?=?134.8793
m?=?135.2400
n?=?142.7200
b?=?142.7200
Specifically as shown in Figure 5, the upper line boundary a of granulation value and b can comprise existing granulation data fully as can be seen from Figure, and n=b in this example, and the granulating method obviously proposed in the present invention is better than existing granulating method.
Be more than the application of single window, if, in a true application, should choose corresponding window value, time series be divided into to the different time periods.Detailed process as shown in Figure 6.
As shown in Figure 6, for original time series to be predicted
, the trend prediction that it is carried out based on Fuzzy Information Granulation comprises the steps:
Step 1, selected window value
, original time series is carried out to discretize, form the window time series
, wherein
, the window seasonal effect in time series length formed is original time series length
with window
take off round values after the phase division operation.
Step 2, for each time series, adopt the Fuzzy Information Granulation trapezoid model towards the time series trend prediction of the present invention to seek the ginseng method series of windows to be carried out to obfuscation one by one, form high layer information grain time series
with
, wherein
,
.Wherein
be exactly to support upper rank b,
support exactly lower bound a.
Step 3, the existing forecast model of employing are predicted the granulation data.Existing be usually used in the seasonal effect in time series forecast model and comprise neural network, SVM etc.
Step 4, draw time series variation trend and numerical value interval.The effect of prediction depends on the forecast model of choosing.
Adopt the Fuzzy Information Granulation trapezoid model towards the time series trend prediction of the present invention to seek the ginseng method and predict that the time series variation trend obtained has significant lifting compared to the conventional information granulating method prediction effect that adopts identical Forecasting Methodology, and have more realistic meaning and practical value.
In sum, these are only preferred embodiment of the present invention, be not intended to limit protection scope of the present invention.Within the spirit and principles in the present invention all, any modification of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.