ARCtan
Copyright 2000 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
The NEURAL Procedure
COMBINATION FUNCTIONS
A combination function combines the values received from preceding nodes into a single number called
the net input. Both output and hidden layers are assigned combination functions.
The following combination functions are available.
Add
Adds all the incoming values without using any weights or biases.
Linear
Is a linear combination of the incoming values and weights.
EQSlopes
Is identical to the Linear combination function, except that the same connection weights are used
for each unit in the layer, although different units have different biases. EQSlopes is mainly used
for ordinal targets.
EQRadial
Is a radial basis function with equal heights and widths for all units in the layer.
EHRadial
Is a radial basis function with equal heights but unequal widths for all units in the layer.
EWRadial
Is a radial basis function with equal widths but unequal heights for all units in the layer.
EVRadial
Is a radial basis function with equal volumes for all units in the layer.
XRadial
Is a radial basis function with unequal heights and widths for all units in the layer.
The following definitions apply to the Table of Combination Functions:
All summations
Are divided by the net inputs indexed by i.
The altitude of the jth unit
The width (bias) of the jth unit
A common bias shared by all units in the layer
The fan-in of the
jth unit
The weight connecting the ith incoming value to the jth unit
The common weight for the ith input shared by all units in the layer
The ith incoming value
Combination Functions
FUNCTION
DEFINITION
ADD
LINear
EQSlopes
XRAdial
EHRadial
EVRadial
EWRadial
EQRadial
RADial
defaults to EHRadial
Copyright 2000 by SAS Institute Inc., Cary, NC, USA. All rights reserved.
The NEURAL Procedure
INITIAL Statement
After a network has been defined in terms of input, hidden and output layers, all weights and
biases in the network must be given initial values before any training is performed. PROC
NEURAL will by default supply appropriate random or computed values for these quantities. If
you train a network without supplying an INITIAL or USE statement, the network will be
initialized using the default specifications.
Category Action Statement - affects the network or the data sets. Options set in an action statement
affect only that statement.
INITIAL <
BIADJUST=
adjustment-value>
<
INEST=
SAS-data-set>
<
INFAN=
number>
<
OUTEST=
SAS-data-set>
<
RANDBIAS|NORANDBIAS>
<
RANDOUT|NORANDOUT>
<
RANDOM=
integer>
<
RANDSCALE | NORANDSCALE>;
Options
BIADJUST= adjustment-value
Specifies how to adjust the random biases for units with a LINEAR combination function. A
random bias is adjusted by multiplying by the function of the weights indicated by
adjustment-value, and dividing by the scale (RANSCALE=) of the distribution from which the
random bias was drawn. adjustment value can be one of the following:
SUM
Adjusts random initial biases for the sum of the absolute connection weights leading into
the unit. This value is typically used with STD=MIDRANGE for inputs and
RANDIST=UNIFORM.
USS
Adjusts random initial biases for the square root of the sum of squared connection weights
leading into the unit. This value is typically used with STD=STD for inputs and
RANDIST=NORMAL.
NONE|NO
No bias adjustment.
Default:
BIADJUST=NONE
INEST=SAS-data-set
Specifies an input data set that contains some or all of the weights. Any weights in the INEST=
data set that have missing values are assigned values according to the RANDOM=, RANDOUT,
and RANDBIAS options, as well as the options that pertain to random number distributions that
you specify in the Random statements. An INEST= data set will typically have been created by
using the OUTEST= option in a SAVE or a TRAIN statement from a previous execution of the
NEURAL procedure.
INFAN=number
Divide random connection weights by
(fan-in of unit)** number
where the "fan-in" of a unit is the number of other units feeding into that unit, not counting the
bias or altitude.
Default:
0 for radial combination functions, otherwise .5
Range:
between 0 and 1
OUTEST=SAS-data-set
Specifies the output data set that contains all the initial weights.
RANDBIAS | NORANDBIAS
Specifies whether to randomize output biases.
Note: NORANDBIAS overrides whatever you specify in the RANOPTIONS statement.
Default:
NORANDBIAS, which sets bias to the inverse activation function of the
target mean.
RANDOM=integer
Specifies the random number seed.
Default:
0
RANDOUT | NORANDOUT
Specifies whether to randomize the output connection weights.
Note: NORANDOUT overrides whatever you specify in the RANOPTIONS statement.
Default:
NORANDOUT, which sets weights to 0.
RANDSCALE | NORANDSCALE
Specifies whether to randomize target scale estimates.