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## -*- texinfo -*-
## @deftypefn  {} {@var{y} =} logspace (@var{a}, @var{b})
## @deftypefnx {} {@var{y} =} logspace (@var{a}, @var{b}, @var{n})
## @deftypefnx {} {@var{y} =} logspace (@var{a}, pi)
## @deftypefnx {} {@var{y} =} logspace (@var{a}, pi, @var{n})
## Return a row vector with @var{n} elements logarithmically spaced from
## @tex
## $10^{a}$ to $10^{b}$.
## @end tex
## @ifnottex
## 10^@var{a} to 10^@var{b}.
## @end ifnottex
##
## If the number of elements @var{n} is unspecified it defaults to 50.
##
## If @var{b} is equal to
## @tex
## $\pi$,
## @end tex
## @ifnottex
## pi,
## @end ifnottex
## the points are between
## @tex
## $10^{a}$ and $\pi$,
## @end tex
## @ifnottex
## 10^@var{a} and pi,
## @end ifnottex
## @emph{not}
## @tex
## $10^{a}$ and $10^{\pi}$,
## @end tex
## @ifnottex
## 10^@var{a} and 10^pi,
## @end ifnottex
## which is useful in digital signal processing.
##
## Programming Notes: For compatibility with @sc{matlab}, return the right-hand
## side of the range
## @tex
## ($10^{b}$)
## @end tex
## @ifnottex
## (10^@var{b})
## @end ifnottex
## when a single value (@var{n} = 1) is requested.
## If @var{n} is not an integer then @code{floor (@var{n})} is used to round
## the number of elements.  If @var{n} is zero or negative then an empty 1x0
## matrix is returned.
## @seealso{linspace}
## @end deftypefn

function y = logspace (a, b, n = 50)

  if (nargin < 2)
    print_usage ();
  endif

  if (! (isscalar (a) && isscalar (b) && isscalar (n)))
    error ("logspace: arguments A, B, and N must be scalars");
  endif

  npoints = fix (n);

  if (b == pi)
    b = log10 (pi);
  endif

  y = 10 .^ (linspace (a, b, npoints));

endfunction


%!test
%! x1 = logspace (1, 2);
%! x2 = logspace (1, 2, 10.1);
%! x3 = logspace (1, -2, 10);
%! x4 = logspace (1, pi, 10);
%! assert (size (x1) == [1, 50]);
%! assert (abs (x1(1) - 10) < eps);
%! assert (abs (x1(50) - 100) < eps);
%! assert (size (x2) == [1, 10]);
%! assert (abs (x2(1) - 10) < eps);
%! assert (abs (x2(10) - 100) < eps);
%! assert (size (x3) == [1, 10]);
%! assert (abs (x3(1) - 10) < eps);
%! assert (abs (x3(10) - 0.01) < eps);
%! assert (size (x4) == [1, 10]);
%! assert (abs (x4(1) - 10) < eps);
%! assert (abs (x4(10) - pi) < sqrt (eps));

## Edge cases
%!assert (logspace (Inf, Inf, 3), [Inf, Inf, Inf])
%!assert (logspace (-Inf, Inf, 3), [0, 1, Inf])
%!testif ; ! __have_feature__ ("LLVM_LIBCXX")
%! assert (logspace (Inf + 1i, Inf + 1i, 3),
%!         repmat (complex (-Inf,Inf), [1, 3]))
%!testif HAVE_LLVM_LIBCXX  <55538>
%! assert (logspace (Inf + 1i, Inf + 1i, 3),
%!         repmat (complex (-Inf,Inf), [1, 3]))
%!testif ; ! __have_feature__ ("LLVM_LIBCXX")
%! assert (logspace (-Inf + 1i, Inf + 1i, 3),
%!         [0, NaN + NaN * 1i, complex(-Inf, Inf)])
%!testif HAVE_LLVM_LIBCXX  <55538>
%! assert (logspace (-Inf + 1i, Inf + 1i, 3),
%!         [0, NaN + NaN * 1i, complex(-Inf, Inf)])
## Octave prefers to return NaN which indicates failure of algorithm.
## Tests can be re-instated if full Matlab-compatibility is coded.
%!#assert (logspace (0, Inf, 3), [1, Inf, Inf])
%!#assert (logspace (0, -Inf, 3), [1, 0, 0])
%!assert (logspace (Inf, -Inf, 3), [Inf, 1, 0])
%!assert (logspace (-Inf, 0, 3), [0, NaN, 1])
%!assert (logspace (Inf, 0, 3), [Inf, NaN, 1])

## Test input validation
%!error <Invalid call> logspace ()
%!error logspace ([1, 2; 3, 4], 5, 6)
%!error logspace (1, [1, 2; 3, 4], 6)
%!error logspace (1, 2, [1, 2; 3, 4])
