1 ## Copyright (C) 2012 Rik Wehbring
2 ## Copyright (C) 1995-2012 Kurt Hornik
4 ## This file is part of Octave.
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7 ## under the terms of the GNU General Public License as published by
8 ## the Free Software Foundation; either version 3 of the License, or (at
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21 ## @deftypefn {Function File} {} expinv (@var{x}, @var{lambda})
22 ## For each element of @var{x}, compute the quantile (the inverse of the
23 ## CDF) at @var{x} of the exponential distribution with mean @var{lambda}.
26 ## Author: KH <Kurt.Hornik@wu-wien.ac.at>
27 ## Description: Quantile function of the exponential distribution
29 function inv = expinv (x, lambda)
35 if (!isscalar (lambda))
36 [retval, x, lambda] = common_size (x, lambda);
38 error ("expinv: X and LAMBDA must be of common size or scalars");
42 if (iscomplex (x) || iscomplex (lambda))
43 error ("expinv: X and LAMBDA must not be complex");
52 if (iscomplex (x) || iscomplex (lambda))
53 error ("expinv: X and LAMBDA must not be complex");
56 if (isa (x, "single") || isa (lambda, "single"))
57 inv = NaN (size (x), "single");
62 k = (x == 1) & (lambda > 0);
65 k = (x >= 0) & (x < 1) & (lambda > 0);
67 inv(k) = - lambda * log (1 - x(k));
69 inv(k) = - lambda(k) .* log (1 - x(k));
76 %! x = [-1 0 0.3934693402873666 1 2];
77 %!assert(expinv (x, 2*ones(1,5)), [NaN 0 1 Inf NaN], eps);
78 %!assert(expinv (x, 2), [NaN 0 1 Inf NaN], eps);
79 %!assert(expinv (x, 2*[1 0 NaN 1 1]), [NaN NaN NaN Inf NaN], eps);
80 %!assert(expinv ([x(1:2) NaN x(4:5)], 2), [NaN 0 NaN Inf NaN], eps);
82 %% Test class of input preserved
83 %!assert(expinv ([x, NaN], 2), [NaN 0 1 Inf NaN NaN], eps);
84 %!assert(expinv (single([x, NaN]), 2), single([NaN 0 1 Inf NaN NaN]), eps);
85 %!assert(expinv ([x, NaN], single(2)), single([NaN 0 1 Inf NaN NaN]), eps);
87 %% Test input validation
90 %!error expinv (1,2,3)
91 %!error expinv (ones(3),ones(2))
92 %!error expinv (ones(2),ones(3))