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## -*- texinfo -*-
## @deftypefn  {} {} meansq (@var{x})
## @deftypefnx {} {} 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 && nargin != 2)
    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 meansq ()
%!error meansq (1, 2, 3)
%!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)