tiling_get.m

approximate reinforcement learning

function [v, i, j] = tiling_get(xdata, wdata, tdim, x, i)
% TILING_GET Computes value of input x in tiling with given prefix
%   [V, I] = TILING_GET(XDATA, WDATA, TDIM, X)
% Parameters:
%   xdata       - tile grid data
%   wdata       - tiling weight data
%   tdim        - tiling dimensionality info
%   x           - the input vector. I can contain only the continuous components, in
%       which case the values of all the discrete inputs are returned in an array. It can
%       contain the complete input, in which case the value of the given discrete input are
%       returned in a scalar.
%   i           - (optional) indices of tiles which fire for x.
%       If these indices are already available, supply them for speed. If these indices are
%       supplied, the value of the continuous inputs is ignored.
% Returns:
%   v           - the value of the complete input x, or the values of all discrete input
%       combinations for the continuous input part x, depending on how x is specified
%   i           - flat indices of the tiles fired by the input
%   j           - flat indices of discrete input components which were retrieved. 1 if no
%       discrete components exist.

if nargin < 5,
    % construct d+1 dimensional indices for the tiles in the c = tdim(1) tilings
    ii = zeros(tdim.c, tdim.cdim + 1);
    ii(:, 1) = 1:tdim.c;       % 1:c on the first column

    % for each input component,
    for di = 1:tdim.cdim,        
        % compute the indices of fired tiles in its tilings
        ii(:, di+1) = sum(xdata{di} <= x(di), 2);
    end;
    i = ndi2lin(ii, tdim.tsize);
end;


if isempty(tdim.dsize),                 % efficient return if no discrete comp
    v = sum(wdata(i)) / tdim.c;
    return;
end;

xd = x(tdim.cdim + 1:end);          % discrete inputs (identified with indices), if any
if isempty(xd),                     % return for all discrete combinations
	v = sum(wdata(i, :));
    if tdim.ddim > 1, v = reshape(v, tdim.dsize); end;
else                                % return for discrete input only
    j = ndi2lin(xd, tdim.dsize);
    v = sum(wdata(i, j));
end;

v = v / tdim.c;

% === END tiling_get, RETURNING v, i, j ======================================================