help spmat idistance
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Title

    spmat idistance -- Create an spmat object containing an inverse-distance
                         spatial-weighting matrix W


Syntax

        spmat idistance objname varlist [if] [in], id(varname) [options]


    options                            Description
    -------------------------------------------------------------------------
    * id(varname)                      ID variable
      dfunction(function[, miles])     distance function
      normalize(norm)                  normalization method
      btruncate(b B)                   bin truncation
      dtruncate(l u)                   diagonal truncation
      vtruncate(#)                     value truncation
      banded                           banded storage
      replace                          replace objname
    -------------------------------------------------------------------------
    * Required
    Only one of btruncate(), dtruncate(), or vtruncate() may be specified.


Description

    spmat idistance puts an inverse-distance spatial-weighting matrix W into
    the new spmat object objname.  The ijth element of W contains the inverse
    of the distance between points i and j calculated from the coordinate
    variables specified in varlist.  Longitude must be specified first if
    coordinate variables represent longitude and latitude.


Options

    id(varname) specifies a numeric variable that contains a unique
        identifier for each observation. This option is required.

    dfunction(function[, miles]) specifies the distance function.  function
        may be one of euclidean (default), dhaversine, rhaversine, or the
        Minkowski distance of order p where p is an integer greater than or
        equal to 1.

        Use dhaversine when your coordinate variables are in degrees; use
        rhaversine when your coordinate variables are in radians.  By
        default, the distances are calculated in kilometers; specify the
        optional miles argument if you want the distances to be calculated in
        miles.

    normalize(norm) specifies the normalization method.  norm may be one of
        row, minmax, or spectral.

    truncate() options specify one of the three available truncation
        criteria.  The values of the spatial-weighting matrix W that meet the
        truncation criterion will be changed to zero.

        btruncate(b B) partitions the value of W into B bins and truncates to
        zero entries that fall into bin b or below.

        dtruncate(l u) truncates to zero the values of W that fall l
        diagonals below and u diagonals above the main diagonal.  Neither
        value can be greater than floor((cols(W)-1)/4).

        vtruncate(#) truncates to zero the values of W that are less than or
        equal to #.

    banded instructs spmat to store the truncated inverse-distance matrix in
        a banded form; see Remarks in spmat tobanded for details.

    replace allows objname to be overwritten if it already exists.


Example

    Setup
        . use pollute

    Create the spmat object dobj containing an inverse-distance matrix
        . spmat idistance dobj longitude latitude, id(id)
            dfunction(dhaversine)


Also see

    Online:  spmat, spreg, spivreg, spmap, shp2dta, mif2dta (if installed)