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1 ## Copyright (C) 1998 Auburn University. All rights reserved. |
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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 ## -*- texinfo -*- |
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20 ## @deftypefn {Function File} {[@var{dsys}, @var{fidx}] =} dmr2d (@var{sys}, @var{idx}, @var{sprefix}, @var{ts2}, @var{cuflg}) |
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21 ## convert a multirate digital system to a single rate digital system |
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22 ## states specified by @var{idx}, @var{sprefix} are sampled at @var{ts2}, all |
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23 ## others are assumed sampled at @var{ts1} = @code{sysgettsam (@var{sys})}. |
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24 ## |
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25 ## @strong{Inputs} |
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26 ## @table @var |
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27 ## @item sys |
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28 ## discrete time system; |
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29 ## @code{dmr2d} exits with an error if @var{sys} is not discrete |
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30 ## @item idx |
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31 ## indices or names of states with sampling time |
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32 ## @code{sysgettsam(@var{sys})} (may be empty); see @code{cellidx} |
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33 ## @item sprefix |
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34 ## list of string prefixes of states with sampling time |
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35 ## @code{sysgettsam(@var{sys})} (may be empty) |
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36 ## @item ts2 |
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37 ## sampling time of states not specified by @var{idx}, @var{sprefix} |
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38 ## must be an integer multiple of @code{sysgettsam(@var{sys})} |
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39 ## @item cuflg |
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40 ## "constant u flag" if @var{cuflg} is nonzero then the system inputs are |
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41 ## assumed to be constant over the revised sampling interval @var{ts2}. |
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42 ## Otherwise, since the inputs can change during the interval |
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43 ## @var{t} in @math{[k ts2, (k+1) ts2]}, an additional set of inputs is |
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44 ## included in the revised B matrix so that these intersample inputs |
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45 ## may be included in the single-rate system. |
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46 ## default @var{cuflg} = 1. |
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47 ## @end table |
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48 ## |
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49 ## @strong{Outputs} |
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50 ## @table @var |
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51 ## @item dsys |
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52 ## equivalent discrete time system with sampling time @var{ts2}. |
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53 ## |
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54 ## The sampling time of sys is updated to @var{ts2}. |
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55 ## |
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56 ## if @var{cuflg}=0 then a set of additional inputs is added to |
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57 ## the system with suffixes _d1, @dots{}, _dn to indicate their |
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58 ## delay from the starting time k @var{ts2}, i.e. |
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59 ## u = [u_1; u_1_d1; @dots{}, u_1_dn] where u_1_dk is the input |
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60 ## k*ts1 units of time after u_1 is sampled. (@var{ts1} is |
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61 ## the original sampling time of the discrete time system and |
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62 ## @var{ts2} = (n+1)*ts1) |
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63 ## |
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64 ## @item fidx |
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65 ## indices of "formerly fast" states specified by @var{idx} and @var{sprefix}; |
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66 ## these states are updated to the new (slower) sampling interval @var{ts2}. |
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67 ## @end table |
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68 ## |
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69 ## @strong{WARNING} Not thoroughly tested yet; especially when |
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70 ## @var{cuflg} == 0. |
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71 ## @end deftypefn |
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72 |
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73 ## Adapted from c2d by a.s.hodel@eng.auburn.edu |
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74 |
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75 function [dsys, fidx] = dmr2d (sys, idx, sprefix, Ts2, cuflg) |
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76 |
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77 ## parse input arguments |
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78 if(nargin != 4 | nargout > 2) |
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79 print_usage (); |
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80 |
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81 elseif (!isstruct(sys)) |
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82 error("sys must be in system data structure form"); |
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83 |
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84 elseif(!is_digital(sys)) |
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85 error("sys must be discrete-time; continuous time passed"); |
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86 |
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87 endif |
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88 |
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89 if(is_signal_list(idx) | ischar(idx)) |
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90 idx = sysidx(sys,"st",idx); |
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91 |
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92 elseif (!(isvector(idx) | isempty(idx))) |
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93 error(["idx(",num2str(rows(idx)),"x",num2str(columns(idx)), ... |
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94 ") must be a vector"]); |
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95 |
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96 elseif (any(idx <= 0)) |
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97 idv = find(idx <= 0); |
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98 ii = idv(1); |
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99 error(["idx(",num2str(ii),")=",num2str(idx(ii)), ... |
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100 "; entries of idx must be positive"]); |
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101 |
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102 elseif(!(is_signal_list(sprefix) | isempty(sprefix))) |
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103 error("sprefix must be a signal list (see is_signal_list) or empty"); |
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104 |
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105 elseif(!is_sample(Ts2)) |
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106 error(["Ts2=",num2str(Ts2),"; invalid sampling time"]); |
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107 |
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108 endif |
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109 |
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110 ## optional argument: cuflg |
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111 if(nargin <= 4) |
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112 cuflg = 1; # default: constant inputs over Ts2 sampling interv. |
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113 elseif( !isscalar(cuflg) ) |
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114 error("cuflg must be a scalar") |
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115 elseif( cuflg != 0 | cuflg != 1) |
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116 error(["cuflg = ",num2str(cuflg),", should be 0 or 1"]); |
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117 endif |
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118 |
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119 ## extract state space information |
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120 [da,db,dc,dd,Ts1,nc,nz,stname,inname,outname,yd] = sys2ss(sys); |
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121 |
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122 ## compute number of steps |
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123 if(Ts1 > Ts2) |
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124 error(["Current sampling time=",num2str(Ts1)," > Ts2=",num2str(Ts2)]); |
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125 endif |
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126 nstp = floor(Ts2/Ts1+0.5); |
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127 if(abs((Ts2 - Ts1*nstp)/Ts1) > 1e-12) |
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128 warning(["dmr2d: Ts1=",num2str(Ts1),", Ts2=",num2str(Ts2), ... |
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129 ", selecting nsteps=",num2str(nstp),"; mismatch"]); |
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130 endif |
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131 |
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132 if(isempty(sprefix) & isempty(idx)) |
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133 warning("both sprefix and idx are empty; returning dsys=sys"); |
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134 fidx = []; |
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135 dsys = sys; |
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136 return |
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137 elseif(isempty(sprefix)) |
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138 fidx = idx; |
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139 else |
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140 fidx = reshape(idx,1,length(idx)); |
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141 ## find states whose name begins with any strings in sprefix. |
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142 ns = length(sprefix); |
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143 for kk=1:ns |
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144 spk = sprefix{kk}; # get next prefix and length |
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145 spl = length(spk); |
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146 |
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147 ## check each state name |
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148 for ii=1:nz |
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149 sti = stname{ii}; # compare spk with this state name |
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150 if(length(sti) >= spl) |
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151 ## if the prefix matches and ii isn't already in the list, add ii |
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152 if(strcmp(sti(1:spl),spk) & !any(fidx == ii) ) |
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153 fidx = sort([fidx,ii]); |
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154 endif |
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155 endif |
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156 endfor |
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157 endfor |
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158 endif |
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159 |
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160 if(nstp == 0) |
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161 warning("dmr2d: nstp = 0; setting tsam and returning"); |
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162 dsys = syschtsam(sys,Ts2); |
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163 return |
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164 elseif(nstp < 0) |
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165 error(["nstp = ", num2str(nstp)," < 0; this shouldn't be!"]); |
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166 endif |
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167 |
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168 ## permute system matrices |
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169 pv = sysreorder(nz,fidx); |
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170 pv = pv(nz:-1:1); # reverse order to put fast modes in leading block |
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171 |
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172 ## construct inverse permutation |
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173 Inz = eye(nz); |
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174 pvi = (Inz(pv,:)'*[1:nz]')'; |
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175 |
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176 ## permute A, B (stname permuted for debugging only) |
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177 da = da(pv,pv); |
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178 db = db(pv,:); |
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179 stname = stname(pv); |
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180 |
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181 ## partition A, B: |
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182 lfidx = length(fidx); |
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183 bki = 1:lfidx; |
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184 a11 = da(bki,bki); |
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185 b1 = db(bki,:); |
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186 |
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187 if(lfidx < nz) |
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188 lfidx1 = lfidx+1; |
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189 bki2 = (lfidx1):nz; |
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190 a12 = da(bki,bki2); |
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191 b2 = db(bki2,:); |
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192 else |
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193 warning("dmr2d: converting entire A,B matrices to new sampling rate"); |
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194 lfidx1 = -1; |
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195 bki2 = []; |
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196 endif |
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197 |
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198 ## begin system conversion: nstp steps |
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199 |
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200 ## compute abar_{n-1}*a12 and appropriate b matrix stuff |
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201 a12b = a12; # running total of abar_{n-1}*a12 |
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202 a12w = a12; # current a11^n*a12 (start with n = 0) |
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203 if(cuflg) |
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204 b1b = b1; |
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205 b1w = b1; |
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206 else |
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207 ## cuflg == 0, need to keep track of intersample inputs too |
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208 nzdx = find(max(abs(b1)) != 0); # FIXME: check tolerance relative to ||b1|| |
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209 b1w = b1(nzdx); |
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210 innamenz = inname(nzdx); |
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211 b1b = b1; # initial b1 must match columns in b2 |
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212 endif |
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213 |
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214 ## compute a11h = a11^nstp by squaring |
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215 a11h = eye(size(a11)); |
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216 p2 = 1; |
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217 a11p2 = a11; #a11^p2 |
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218 |
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219 nstpw = nstp; # workspace for computing a11^nstp |
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220 while(nstpw > 0.5) |
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221 oddv = rem(nstpw,2); |
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222 if(oddv) |
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223 a11h = a11h*a11p2; |
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224 endif |
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225 nstpw = (nstpw-oddv)/2; |
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226 if(nstpw > 0.5) |
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227 a11p2 = a11p2*a11p2; # a11^(next power of 2) |
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228 endif |
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229 endwhile |
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230 |
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231 ## FIXME: this part should probably also use squaring, but |
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232 ## that would require exponentially growing memory. What do do? |
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233 for kk=2:nstp |
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234 ## update a12 block to sum(a12 + ... + a11^(kk-1)*a12) |
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235 a12w = a11*a12w; |
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236 a12b = a12b + a12w; |
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237 |
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238 ## similar for b1 block (checking for cuflg first!) |
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239 b1w = a11*b1w; |
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240 if(cuflg) |
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241 b1b = b1b + b1w; # update b1 block just like we did a12 |
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242 else |
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243 b1b = [b1b, b1w]; # append new inputs |
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244 newin = strappend(innamenz,["_d",num2str(kk-1)]); |
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245 inname = __sysconcat__(inname,newin); |
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246 endif |
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247 endfor |
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248 |
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249 ## reconstruct system and return |
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250 da(bki,bki) = a11h; |
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251 db(bki,1:columns(b1b)) = b1b; |
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252 if(!isempty(bki2)) |
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253 da(bki,bki2) = a12b; |
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254 endif |
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255 |
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256 da = da(pvi,pvi); |
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257 db = db(pvi,:); |
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258 stname = stname(pvi); |
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259 |
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260 ## construct new system and return |
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261 dsys = ss(da,db,dc,dd,Ts2,0,nz,stname,inname,outname,find(yd == 1)); |
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262 |
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263 endfunction |
