annotate scripts/statistics/distributions/poissinv.m @ 20644:4e307c55a2b5

Use isempty () rather than any () for faster code in inverse statistical distributions. betainv.m, binoinv.m, gaminv.m, poissinv.m: Use '! isempty (k)' rather than 'any (k)' for faster code.
author Rik <rik@octave.org>
date Sun, 11 Oct 2015 21:09:41 -0700
parents b3f56ed8d1f9
children
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1 ## Copyright (C) 1995-2015 Kurt Hornik
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2 ## Copyright (C) 2015 Lachlan Andrew
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3 ## Copyright (C) 2014 Mike Giles
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4 ## Copyright (C) 2012 Rik Wehbring
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5 ##
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6 ## This file is part of Octave.
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7 ##
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8 ## Octave is free software; you can redistribute it and/or modify it
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9 ## under the terms of the GNU General Public License as published by
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10 ## the Free Software Foundation; either version 3 of the License, or (at
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11 ## your option) any later version.
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12 ##
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13 ## Octave is distributed in the hope that it will be useful, but
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14 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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15 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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16 ## General Public License for more details.
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17 ##
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18 ## You should have received a copy of the GNU General Public License
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19 ## along with Octave; see the file COPYING. If not, see
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20 ## <http://www.gnu.org/licenses/>.
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21
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22 ## -*- texinfo -*-
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23 ## @deftypefn {Function File} {} poissinv (@var{x}, @var{lambda})
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24 ## For each element of @var{x}, compute the quantile (the inverse of the CDF)
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25 ## at @var{x} of the Poisson distribution with parameter @var{lambda}.
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26 ## @end deftypefn
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27
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28 ## Author: Lachlan <lachlanbis@gmail.com>
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29 ## based on code by
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30 ## KH <Kurt.Hornik@wu-wien.ac.at>
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31 ## Mike Giles <mike.giles@maths.ox.ac.uk>
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32 ## Description: Quantile function of the Poisson distribution
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33
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34 function inv = poissinv (x, lambda)
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35
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36 if (nargin != 2)
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37 print_usage ();
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38 endif
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39
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40 if (! isscalar (lambda))
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41 [retval, x, lambda] = common_size (x, lambda);
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42 if (retval > 0)
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43 error ("poissinv: X and LAMBDA must be of common size or scalars");
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44 endif
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45 endif
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46
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47 if (iscomplex (x) || iscomplex (lambda))
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48 error ("poissinv: X and LAMBDA must not be complex");
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49 endif
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50
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51 if (isa (x, "single") || isa (lambda, "single"))
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52 inv = zeros (size (x), "single");
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53 else
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54 inv = zeros (size (x));
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55 endif
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56
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57 k = (x < 0) | (x > 1) | isnan (x) | !(lambda > 0);
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58 inv(k) = NaN;
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59
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60 k = (x == 1) & (lambda > 0);
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61 inv(k) = Inf;
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62
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63 k = (x > 0) & (x < 1) & (lambda > 0);
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64 if (any (k(:)))
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65 limit = 20; # After 'limit' iterations, use approx
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66 if (isscalar (lambda))
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67 cdf = [(cumsum (poisspdf (0:limit-1,lambda))), 2];
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68 y = x(:); # force to column
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69 r = bsxfun (@le, y(k), cdf);
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70 [~, inv(k)] = max (r, [], 2); # find first instance of x <= cdf
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71 inv(k) -= 1;
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72 else
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73 kk = find (k);
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74 cdf = exp (-lambda(kk));
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75 for i = 1:limit
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76 m = find (cdf < x(kk));
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77 if (isempty (m))
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78 break;
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79 else
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80 inv(kk(m)) += 1;
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81 cdf(m) += poisspdf (i, lambda(kk(m)));
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82 endif
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83 endfor
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84 endif
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85
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86 ## Use Mike Giles's magic when inv isn't < limit
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87 k &= (inv == limit);
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88 if (any (k(:)))
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89 if (isscalar (lambda))
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90 lam = repmat (lambda, size (x));
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91 else
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92 lam = lambda;
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93 endif
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94 inv(k) = analytic_approx (x(k), lam(k));
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95 endif
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96 endif
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97
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98 endfunction
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99
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100
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101 ## The following is based on Mike Giles's CUDA implementation,
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102 ## [http://people.maths.ox.ac.uk/gilesm/codes/poissinv/poissinv_cuda.h]
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103 ## which is copyright by the University of Oxford
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104 ## and is provided under the terms of the GNU GPLv3 license:
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105 ## http://www.gnu.org/licenses/gpl.html
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106
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107 function inv = analytic_approx (x, lambda)
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108 s = norminv (x, 0, 1) ./ sqrt (lambda);
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109 k = (s > -0.6833501) & (s < 1.777993);
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110 ## use polynomial approximations in central region
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111 if (any (k))
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112 lam = lambda(k);
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113 if (isscalar (s))
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114 sk = s;
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115 else
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116 sk = s(k);
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117 endif
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118
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119 ## polynomial approximation to f^{-1}(s) - 1
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120 rm = 2.82298751e-07;
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121 rm = -2.58136133e-06 + rm.*sk;
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122 rm = 1.02118025e-05 + rm.*sk;
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123 rm = -2.37996199e-05 + rm.*sk;
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124 rm = 4.05347462e-05 + rm.*sk;
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125 rm = -6.63730967e-05 + rm.*sk;
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126 rm = 0.000124762566 + rm.*sk;
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127 rm = -0.000256970731 + rm.*sk;
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128 rm = 0.000558953132 + rm.*sk;
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129 rm = -0.00133129194 + rm.*sk;
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130 rm = 0.00370367937 + rm.*sk;
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131 rm = -0.0138888706 + rm.*sk;
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132 rm = 0.166666667 + rm.*sk;
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133 rm = sk + sk.*(rm.*sk);
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134
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135 ## polynomial approximation to correction c0(r)
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136
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137 t = 1.86386867e-05;
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138 t = -0.000207319499 + t.*rm;
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139 t = 0.0009689451 + t.*rm;
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140 t = -0.00247340054 + t.*rm;
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141 t = 0.00379952985 + t.*rm;
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142 t = -0.00386717047 + t.*rm;
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143 t = 0.00346960934 + t.*rm;
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144 t = -0.00414125511 + t.*rm;
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145 t = 0.00586752093 + t.*rm;
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146 t = -0.00838583787 + t.*rm;
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147 t = 0.0132793933 + t.*rm;
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148 t = -0.027775536 + t.*rm;
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149 t = 0.333333333 + t.*rm;
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150
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151 ## O(1/lam) correction
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152
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153 y = -0.00014585224;
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154 y = 0.00146121529 + y.*rm;
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155 y = -0.00610328845 + y.*rm;
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156 y = 0.0138117964 + y.*rm;
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157 y = -0.0186988746 + y.*rm;
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158 y = 0.0168155118 + y.*rm;
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159 y = -0.013394797 + y.*rm;
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160 y = 0.0135698573 + y.*rm;
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161 y = -0.0155377333 + y.*rm;
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162 y = 0.0174065334 + y.*rm;
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163 y = -0.0198011178 + y.*rm;
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164 y ./= lam;
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165
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166 inv(k) = floor (lam + (y+t)+lam.*rm);
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167 endif
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168
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169 k = !k & (s > -sqrt (2));
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170 if (any (k))
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171 ## Newton iteration
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172 r = 1 + s(k);
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173 r2 = r + 1;
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174 while (any (abs (r - r2) > 1e-5))
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175 t = log (r);
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176 r2 = r;
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177 s2 = sqrt (2 * ((1-r) + r.*t));
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178 s2(r<1) *= -1;
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179 r = r2 - (s2 - s(k)) .* s2 ./ t;
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180 if (r < 0.1 * r2)
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181 r = 0.1 * r2;
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182 endif
20485
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183 endwhile
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184 t = log (r);
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185 y = lambda(k) .* r + log (sqrt (2*r.*((1-r) + r.*t)) ./ abs (r-1)) ./ t;
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186 inv(k) = floor (y - 0.0218 ./ (y + 0.065 * lambda(k)));
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187 endif
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188
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189 endfunction
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190
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191
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192 %!shared x
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193 %! x = [-1 0 0.5 1 2];
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194 %!assert (poissinv (x, ones (1,5)), [NaN 0 1 Inf NaN])
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195 %!assert (poissinv (x, 1), [NaN 0 1 Inf NaN])
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196 %!assert (poissinv (x, [1 0 NaN 1 1]), [NaN NaN NaN Inf NaN])
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197 %!assert (poissinv ([x(1:2) NaN x(4:5)], 1), [NaN 0 NaN Inf NaN])
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198
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199 ## Test class of input preserved
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200 %!assert (poissinv ([x, NaN], 1), [NaN 0 1 Inf NaN NaN])
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201 %!assert (poissinv (single ([x, NaN]), 1), single ([NaN 0 1 Inf NaN NaN]))
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202 %!assert (poissinv ([x, NaN], single (1)), single ([NaN 0 1 Inf NaN NaN]))
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203
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204 ## Test input validation
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205 %!error poissinv ()
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206 %!error poissinv (1)
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207 %!error poissinv (1,2,3)
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208 %!error poissinv (ones (3), ones (2))
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209 %!error poissinv (ones (2), ones (3))
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210 %!error poissinv (i, 2)
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211 %!error poissinv (2, i)
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212