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########################################################################
##
## Copyright (C) 1995-2024 The Octave Project Developers
##
## See the file COPYRIGHT.md in the top-level directory of this
## distribution or <https://octave.org/copyright/>.
##
## This file is part of Octave.
##
## Octave is free software: you can redistribute it and/or modify it
## under the terms of the GNU General Public License as published by
## the Free Software Foundation, either version 3 of the License, or
## (at your option) any later version.
##
## Octave is distributed in the hope that it will be useful, but
## WITHOUT ANY WARRANTY; without even the implied warranty of
## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
## GNU General Public License for more details.
##
## You should have received a copy of the GNU General Public License
## along with Octave; see the file COPYING. If not, see
## <https://www.gnu.org/licenses/>.
##
########################################################################
## -*- texinfo -*-
## @deftypefn {} {@var{y} =} meansq (@var{x})
## @deftypefnx {} {@var{y} =} meansq (@var{x}, @var{dim})
## Compute the mean square of the elements of the vector @var{x}.
##
## The mean square is defined as
## @tex
## $$
## {\rm meansq} (x) = {\sum_{i=1}^N {x_i}^2 \over N}
## $$
## where $N$ is the number of elements of @var{x}.
##
## @end tex
## @ifnottex
##
## @example
## @group
## meansq (@var{x}) = 1/N SUM_i @var{x}(i)^2
## @end group
## @end example
##
## @noindent
## where @math{N} is the length of the @var{x} vector.
##
## @end ifnottex
## If @var{x} is a matrix, return a row vector containing the mean square
## of each column.
##
## If the optional argument @var{dim} is given, operate along this dimension.
## @seealso{var, std, moment}
## @end deftypefn
function y = meansq (x, dim)
if (nargin < 1)
print_usage ();
endif
if (! (isnumeric (x) || islogical (x)))
error ("mean: X must be a numeric vector or matrix");
endif
nd = ndims (x);
sz = size (x);
if (nargin < 2)
## Find the first non-singleton dimension.
(dim = find (sz > 1, 1)) || (dim = 1);
else
if (! (isscalar (dim) && dim == fix (dim) && dim > 0))
error ("mean: DIM must be an integer and a valid dimension");
endif
endif
y = sumsq (x, dim) / size (x, dim);
endfunction
%!assert (meansq (1:5), 11)
%!assert (meansq (single (1:5)), single (11))
%!assert (meansq (magic (4)), [94.5, 92.5, 92.5, 94.5])
%!assert (meansq (magic (4), 2), [109.5; 77.5; 77.5; 109.5])
%!assert (meansq ([1 2], 3), [1 4])
## Test input validation
%!error <Invalid call> meansq ()
%!error <X must be a numeric> meansq (['A'; 'B'])
%!error <DIM must be an integer> meansq (1, ones (2,2))
%!error <DIM must be an integer> meansq (1, 1.5)
%!error <DIM must be .* a valid dimension> meansq (1, 0)
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