%SEMIVARIOGRAM   Computes the semivariogram of the field
%
% SYNOPSIS:
%  distribution = semivariogram(image_in,mask,probes,length,estimator)
%
% PARAMETERS:
%  image_in:   defines the phases on which the pair correlation function is computed.
%              image_in can be a binary or labeled image.
%  mask:       mask image to select the regions in image_in that are used to compute the
%              correlation function.
%  probes:     the number of random pairs that are generated to compute the correlation
%              function.
%  length:     the maximum length (in pixels) of the correlation function.
%  estimator:  type of correlation estimator used: 'random' or 'grid'.
%
% EXPLANATION:
%  The semivariogram is half the variance of the difference between two points at a distance D.
%  D is varied from 0 to LENGTH.
%  The function is estimated by probing PROBES pairs in the image. If the estimator
%  is 'random', pairs are selected randomly. If the estimator is 'grid', pairs are
%  selected using a grid.
%
%  The output DISTRIBUTION is an array where the first column is the distance D, and
%  the second column is the semivariogram function samples.
%
% DEFAULTS:
%  image_mask = []
%  probes = 1000000
%  length = 100
%  estimator = 'random'

% (c)2018, Cris Luengo.
% Based on original DIPlib code: (c)1995-2014, Delft University of Technology.
% Based on original DIPimage code: (c)1999-2014, Delft University of Technology.
%
% Licensed under the Apache License, Version 2.0 (the "License");
% you may not use this file except in compliance with the License.
% You may obtain a copy of the License at
%
%    http://www.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS,
% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
% See the License for the specific language governing permissions and
% limitations under the License.
