%                             wdop1.m
%  Scope:   This MATLAB macro computes weighted dilution of precision (WDOP) 
%           quantities when at least three line-of-sight unit vectors are 
%           specified, by using a direct method.
%  Remark:  When less than four line-of-sight unit vectors are specified
%           the computation is not fully significant, and it is conducted
%           by using a pseudoinverse matrix instead of an inverse matrix.
%  Usage:   wdops = wdop1(g,wf)
%  Description of parameters:
%           g     - input, line-of-sight unit vectors, each vector is
%                   stored in another row (it should be 3 columns)
%           wf    - input, array containing weighting factors, it should be
%                   one weighting factor for each line-of-sight unit vector
%                   (in the same order)
%           wdops - output, weighted dilution of precision quantities 
%                   wdops(1) = weighted geometric dilution of precision (WGDOP) 
%                   wdops(2) = weighted position dilution of precision (WPDOP)
%                   wdops(3) = weighted horizontal dilution of precision (WHDOP)
%                   wdops(4) = weighted vertical dilution of precision (WVDOP)
%                   wdops(5) = weighted time dilution of precision (WTDOP)
%  Last update:  06/14/00
%  Copyright (C) 1996-00 by LL Consulting. All Rights Reserved.

function   wdops = wdop1(g,wf)

[nrow,ncol] = size(g);
if (ncol ~= 3) | (nrow < 3)
   error('Error -  WDOP1; check the unit line of sight vectors');
end
if nrow ~= length(wf)
   error('Error -  WDOP1; check the dimension of the weighting factors');
end

unitvec = ones(nrow,1);

h = [g unitvec];                              %  form the matrix  H

%  Determine WDOP quantities

for k = 1:nrow                                %  form the matrix  wf * H
   htemp(k,:) = wf(k) * h(k,:);
end

if nrow >= 4
   wdop = inv(h'* htemp);
else
   wdop = pinv(h'* htemp);
end

wdops(1) = sqrt(wdop(1,1) + wdop(2,2) + wdop(3,3) + wdop(4,4));    %  WGDOP
wdops(2) = sqrt(wdop(1,1) + wdop(2,2) + wdop(3,3));                %  WPDOP
wdops(3) = sqrt(wdop(1,1) + wdop(2,2));                            %  WHDOP
wdops(4) = sqrt(wdop(3,3));                                        %  WVDOP 
wdops(5) = sqrt(wdop(4,4));                                        %  WTDOP