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Dataplot Vol 2 Vol 1

DEX CHECK CENTER POINTS

Name:
    DEX CHECK CENTER POINTS (LET)
Type:
    Let Subcommand
Purpose:
    Given a list of factor variables, create a tag variable that will identify center points.
Description:
    With the 10-step analysis of full and fractional factorial designs, it is helpful to identify which rows of the data are center points and which are not (most of the steps do not include the center points while others, specifically the contour plot, do use the center points).

    For 2-level full or fractional factorial design, the low level is typically coded as "-1" and the upper level is typically coded as "+1". Center points are typically coded as "0". In some cases, the data may be in the original units rather than the coded units.

    This command uses the following algorithm to determine whether a given row is a center point.

    1. For each column, compute the median of the distinct values in that column. This median is used so that the data can be in either coded or original units. Note that if there are an even number of distinct values, none of the rows will match the median. This is reasonable as center points only make sense if there are an odd number of distinct values.

    2. For a given row, if the values for each column are equal to their respective medians, the point is identified as a center point.
Syntax:
    LET <tag> = DEX CHECK CENTER POINT <name1> <name2> ... <namek>
    where <name1> <name2> ... <namek> is a list of 1 to k variable names;
    and where <tag> is a variable where the center point status is' saved.

    All of the variables on the right hand side should be of the same length. These should be the factor variables of the design matrix. Do not include the response variable.

    If a given row of the design matrix is identified as a center point, the corresponding row of will be set to 0. Otherwise, it will be set to 1.

    This TAG variable can be used to subset out the center point when needed.

Examples:
    LET TAG = DEX CHECK CENTER POINT X1 X2 X3
    LET TAG = DEX CHECK CENTER POINT X1 X2 X3 X4 X5
Note:
    The TO syntax is not supported for this command. That is,

      LET TAG = DEX CHECK CENTER POINT X1 TO X5

    should be coded as

      LET STALL = STRING COMBINE X1 TO X5
      LET IFLAG = DEX CHECK CENTER POINT ^STALL
Note:
    Not all design matrices will contain center points. If you want to determine whether or not center points are present, do something like

      LET TAG = DEX CHECK CENTER POINTS X1 X2 X3 X4 X5
      LET NCENT = SIZE TAG SUBSET TAG = 0

    If NCENT is equal to 0, then no center points are present.

Default:
    None
Synonyms:
    None
Related Commands: Applications:
    Analysis of full and fractional factorial designs
Implementation Date:
    2018/10
Program:
     
    let k = 8
    skip 25
    read scott_8_16.dat y x1 to x^k
    let stall = string combine x1 to x^k
    let tag = dex check center point ^stall
    set write decimals 0
    print x1 to x^k tag
        
    The following output is returned
     
    ---------------------------------------------------------------------------------------------------------------------------------------
                 X1             X2             X3             X4             X5             X6             X7             X8            TAG
    ---------------------------------------------------------------------------------------------------------------------------------------
                 -1             -1             -1             -1             -1             -1             -1             -1              1
                  1             -1             -1             -1             -1              1              1              1              1
                 -1              1             -1             -1              1             -1              1              1              1
                  1              1             -1             -1              1              1             -1             -1              1
                 -1             -1              1             -1              1              1              1             -1              1
                  1             -1              1             -1              1             -1             -1              1              1
                 -1              1              1             -1             -1              1             -1              1              1
                  1              1              1             -1             -1             -1              1             -1              1
                 -1             -1             -1              1              1              1             -1              1              1
                  1             -1             -1              1              1             -1              1             -1              1
                 -1              1             -1              1             -1              1              1             -1              1
                  1              1             -1              1             -1             -1             -1              1              1
                 -1             -1              1              1             -1             -1              1              1              1
                  1             -1              1              1             -1              1             -1             -1              1
                 -1              1              1              1              1             -1             -1             -1              1
                  1              1              1              1              1              1              1              1              1
     
        

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Date created: 10/16/2018
Last updated: 10/16/2018

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