annotate scripts/optimization/fminbnd.m @ 17521:c3a3532e3d98

linsolve.m: Add new function for Matlab compatibility. * scripts/linear-algebra/linsolve.m: New function. * scripts/linear-algebra/module.mk: Add linsolve.m to build system. * NEWS: Announce new function.
author Nir Krakauer < nkrakauer@ccny.cuny.edu>
date Thu, 26 Sep 2013 08:30:26 -0700
parents b81b9d079515
children
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1 ## Copyright (C) 2008-2012 VZLU Prague, a.s.
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2 ##
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3 ## This file is part of Octave.
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4 ##
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5 ## Octave is free software; you can redistribute it and/or modify it
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6 ## under the terms of the GNU General Public License as published by
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7 ## the Free Software Foundation; either version 3 of the License, or (at
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8 ## your option) any later version.
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9 ##
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10 ## Octave is distributed in the hope that it will be useful, but
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11 ## WITHOUT ANY WARRANTY; without even the implied warranty of
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12 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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13 ## General Public License for more details.
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14 ##
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15 ## You should have received a copy of the GNU General Public License
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16 ## along with Octave; see the file COPYING. If not, see
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17 ## <http://www.gnu.org/licenses/>.
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18 ##
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19 ## Author: Jaroslav Hajek <highegg@gmail.com>
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20
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21 ## -*- texinfo -*-
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22 ## @deftypefn {Function File} {[@var{x}, @var{fval}, @var{info}, @var{output}] =} fminbnd (@var{fun}, @var{a}, @var{b}, @var{options})
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23 ## Find a minimum point of a univariate function.
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24 ##
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25 ## @var{fun} should be a function handle or name. @var{a}, @var{b} specify a
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26 ## starting interval. @var{options} is a structure specifying additional
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27 ## options. Currently, @code{fminbnd} recognizes these options:
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28 ## @qcode{"FunValCheck"}, @qcode{"OutputFcn"}, @qcode{"TolX"},
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29 ## @qcode{"MaxIter"}, @qcode{"MaxFunEvals"}. For a description of these
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30 ## options, see @ref{XREFoptimset,,optimset}.
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31 ##
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32 ## On exit, the function returns @var{x}, the approximate minimum point
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33 ## and @var{fval}, the function value thereof.
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34 ## @var{info} is an exit flag that can have these values:
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35 ##
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36 ## @itemize
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37 ## @item 1
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38 ## The algorithm converged to a solution.
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39 ##
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40 ## @item 0
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41 ## Maximum number of iterations or function evaluations has been exhausted.
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42 ##
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43 ## @item -1
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44 ## The algorithm has been terminated from user output function.
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45 ## @end itemize
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46 ##
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47 ## Notes: The search for a minimum is restricted to be in the interval
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48 ## bound by @var{a} and @var{b}. If you only have an initial point
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49 ## to begin searching from you will need to use an unconstrained
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50 ## minimization algorithm such as @code{fminunc} or @code{fminsearch}.
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51 ## @code{fminbnd} internally uses a Golden Section search strategy.
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52 ## @seealso{fzero, fminunc, fminsearch, optimset}
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53 ## @end deftypefn
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54
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55 ## This is patterned after opt/fmin.f from Netlib, which in turn is taken from
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56 ## Richard Brent: Algorithms For Minimization Without Derivatives, Prentice-Hall (1973)
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57
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58 ## PKG_ADD: ## Discard result to avoid polluting workspace with ans at startup.
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59 ## PKG_ADD: [~] = __all_opts__ ("fminbnd");
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60
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61 function [x, fval, info, output] = fminbnd (fun, xmin, xmax, options = struct ())
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62
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63 ## Get default options if requested.
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64 if (nargin == 1 && ischar (fun) && strcmp (fun, 'defaults'))
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65 x = optimset ("MaxIter", Inf, "MaxFunEvals", Inf, "TolX", 1e-8,
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66 "OutputFcn", [], "FunValCheck", "off");
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67 return;
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68 endif
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69
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70 if (nargin < 2 || nargin > 4)
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71 print_usage ();
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72 endif
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73
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74 if (ischar (fun))
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75 fun = str2func (fun, "global");
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76 endif
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77
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78 displ = optimget (options, "Display", "notify");
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79 funvalchk = strcmpi (optimget (options, "FunValCheck", "off"), "on");
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80 outfcn = optimget (options, "OutputFcn");
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81 tolx = optimget (options, "TolX", 1e-8);
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82 maxiter = optimget (options, "MaxIter", Inf);
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83 maxfev = optimget (options, "MaxFunEvals", Inf);
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84
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85 if (funvalchk)
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86 ## Replace fun with a guarded version.
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87 fun = @(x) guarded_eval (fun, x);
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88 endif
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89
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90 ## The default exit flag if exceeded number of iterations.
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91 info = 0;
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92 niter = 0;
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93 nfev = 0;
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94 sqrteps = eps (class (xmin + xmax));
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95
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96 c = 0.5*(3 - sqrt (5));
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97 a = xmin; b = xmax;
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98 v = a + c*(b-a);
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99 w = x = v;
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100 e = 0;
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101 fv = fw = fval = fun (x);
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102 nfev++;
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103
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104 ## Only for display purposes.
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105 iter(1).funccount = nfev;
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106 iter(1).x = x;
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107 iter(1).fx = fval;
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108
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109 while (niter < maxiter && nfev < maxfev)
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110 xm = 0.5*(a+b);
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111 ## FIXME: the golden section search can actually get closer than sqrt(eps)
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112 ## sometimes. Sometimes not, it depends on the function. This is the
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113 ## strategy from the Netlib code. Something yet smarter would be good.
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114 tol = 2 * sqrteps * abs (x) + tolx / 3;
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115 if (abs (x - xm) <= (2*tol - 0.5*(b-a)))
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116 info = 1;
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117 break;
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118 endif
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119
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120 if (abs (e) > tol)
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121 dogs = false;
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122 ## Try inverse parabolic step.
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123 iter(niter+1).procedure = "parabolic";
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124
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125 r = (x - w)*(fval - fv);
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126 q = (x - v)*(fval - fw);
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127 p = (x - v)*q - (x - w)*r;
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128 q = 2*(q - r);
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129 p *= -sign (q);
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130 q = abs (q);
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131 r = e;
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132 e = d;
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133
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134 if (abs (p) < abs (0.5*q*r) && p > q*(a-x) && p < q*(b-x))
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135 ## The parabolic step is acceptable.
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136 d = p / q;
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137 u = x + d;
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138
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139 ## f must not be evaluated too close to ax or bx.
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140 if (min (u-a, b-u) < 2*tol)
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141 d = tol * (sign (xm - x) + (xm == x));
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142 endif
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143 else
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144 dogs = true;
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145 endif
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146 else
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147 dogs = true;
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148 endif
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149 if (dogs)
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150 ## Default to golden section step.
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151
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152 ## WARNING: This is also the "initial" procedure following
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153 ## MATLAB nomenclature. After the loop we'll fix the string
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154 ## for the first step.
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155 iter(niter+1).procedure = "golden";
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156
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157 e = ifelse (x >= xm, a - x, b - x);
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158 d = c * e;
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159 endif
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160
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161 ## f must not be evaluated too close to x.
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162 u = x + max (abs (d), tol) * (sign (d) + (d == 0));
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163 fu = fun (u);
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164
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165 niter++;
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166
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167 iter(niter).funccount = nfev++;
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168 iter(niter).x = u;
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169 iter(niter).fx = fu;
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170
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171 ## update a, b, v, w, and x
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172
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173 if (fu <= fval)
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174 if (u < x)
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175 b = x;
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176 else
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177 a = x;
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178 endif
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179 v = w; fv = fw;
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180 w = x; fw = fval;
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181 x = u; fval = fu;
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182 else
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183 ## The following if-statement was originally executed even if fu == fval.
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184 if (u < x)
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185 a = u;
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186 else
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187 b = u;
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188 endif
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189 if (fu <= fw || w == x)
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190 v = w; fv = fw;
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191 w = u; fw = fu;
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192 elseif (fu <= fv || v == x || v == w)
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193 v = u;
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194 fv = fu;
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195 endif
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196 endif
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197
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198 ## If there's an output function, use it now.
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199 if (outfcn)
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200 optv.funccount = nfev;
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201 optv.fval = fval;
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202 optv.iteration = niter;
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203 if (outfcn (x, optv, "iter"))
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204 info = -1;
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205 break;
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206 endif
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207 endif
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208 endwhile
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209
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210 ## Fix the first step procedure.
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211 iter(1).procedure = "initial";
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212
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213 ## Handle the "Display" option
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214 switch (displ)
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215 case "iter"
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216 print_formatted_table (iter);
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217 print_exit_msg (info, struct("TolX", tolx, "fx", fval));
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218 case "notify"
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219 if (info == 0)
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220 print_exit_msg (info, struct("fx",fval));
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221 endif
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222 case "final"
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223 print_exit_msg (info, struct("TolX", tolx, "fx", fval));
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224 case "off"
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225 "skip";
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226 otherwise
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227 warning ("unknown option for Display: '%s'", displ);
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228 endswitch
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229
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230 output.iterations = niter;
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231 output.funcCount = nfev;
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232 output.bracket = [a, b];
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233 ## FIXME: bracketf possibly unavailable.
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234
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235 endfunction
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236
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237 ## An assistant function that evaluates a function handle and checks for
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238 ## bad results.
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239 function fx = guarded_eval (fun, x)
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240 fx = fun (x);
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241 fx = fx(1);
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242 if (! isreal (fx))
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243 error ("fminbnd:notreal", "fminbnd: non-real value encountered");
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244 elseif (isnan (fx))
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245 error ("fminbnd:isnan", "fminbnd: NaN value encountered");
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246 endif
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247 endfunction
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248
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249 ## A hack for printing a formatted table
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250 function print_formatted_table (table)
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251 printf ("\n Func-count x f(x) Procedure\n");
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252 for row=table
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253 printf("%5.5s %7.7s %8.8s\t%s\n",
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254 int2str (row.funccount), num2str (row.x,"%.5f"),
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255 num2str (row.fx,"%.6f"), row.procedure);
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256 endfor
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257 printf ("\n");
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258 endfunction
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259
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260 ## Print either a success termination message or bad news
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261 function print_exit_msg (info, opt=struct())
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262 printf ("");
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263 switch (info)
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264 case 1
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265 printf ("Optimization terminated:\n");
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266 printf (" the current x satisfies the termination criteria using OPTIONS.TolX of %e\n", opt.TolX);
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267 case 0
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268 printf ("Exiting: Maximum number of iterations has been exceeded\n");
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269 printf (" - increase MaxIter option.\n");
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270 printf (" Current function value: %.6f\n", opt.fx);
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271 case -1
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272 "FIXME"; # FIXME: what's the message MATLAB prints for this case?
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273 otherwise
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274 error ("internal error - fminbnd() is bug, sorry!");
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275 endswitch
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276 printf ("\n");
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277 endfunction
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278
14363
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279
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280 %!shared opt0
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281 %! opt0 = optimset ("tolx", 0);
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282 %!assert (fminbnd (@cos, pi/2, 3*pi/2, opt0), pi, 10*sqrt (eps))
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283 %!assert (fminbnd (@(x) (x - 1e-3)^4, -1, 1, opt0), 1e-3, 10e-3*sqrt (eps))
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284 %!assert (fminbnd (@(x) abs (x-1e7), 0, 1e10, opt0), 1e7, 10e7*sqrt (eps))
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285 %!assert (fminbnd (@(x) x^2 + sin (2*pi*x), 0.4, 1, opt0), fzero (@(x) 2*x + 2*pi*cos (2*pi*x), [0.4, 1], opt0), sqrt (eps))
f3d52523cde1 Use Octave coding conventions in all m-file %!test blocks
Rik <octave@nomad.inbox5.com>
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