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1 ## Copyright (C) 1996, 2000, 2004, 2005, 2007 |
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2 ## Auburn University. All rights reserved. |
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3 ## |
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4 ## This file is part of Octave. |
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5 ## |
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6 ## Octave is free software; you can redistribute it and/or modify it |
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7 ## under the terms of the GNU General Public License as published by |
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8 ## the Free Software Foundation; either version 3 of the License, or (at |
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9 ## your option) any later version. |
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10 ## |
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11 ## Octave is distributed in the hope that it will be useful, but |
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12 ## WITHOUT ANY WARRANTY; without even the implied warranty of |
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13 ## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
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14 ## General Public License for more details. |
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15 ## |
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16 ## You should have received a copy of the GNU General Public License |
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17 ## along with Octave; see the file COPYING. If not, see |
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18 ## <http://www.gnu.org/licenses/>. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {[@var{num}, @var{den}] =} ss2tf (@var{a}, @var{b}, @var{c}, @var{d}) |
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22 ## Conversion from transfer function to state-space. |
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23 ## The state space system: |
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24 ## @iftex |
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25 ## @tex |
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26 ## $$ \dot x = Ax + Bu $$ |
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27 ## $$ y = Cx + Du $$ |
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28 ## @end tex |
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29 ## @end iftex |
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30 ## @ifinfo |
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31 ## @example |
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32 ## . |
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33 ## x = Ax + Bu |
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34 ## y = Cx + Du |
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35 ## @end example |
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36 ## @end ifinfo |
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37 ## |
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38 ## is converted to a transfer function: |
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39 ## @iftex |
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40 ## @tex |
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41 ## $$ G(s) = { { \rm num }(s) \over { \rm den }(s) } $$ |
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42 ## @end tex |
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43 ## @end iftex |
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44 ## @ifinfo |
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45 ## @example |
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46 ## |
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47 ## num(s) |
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48 ## G(s)=------- |
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49 ## den(s) |
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50 ## @end example |
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51 ## @end ifinfo |
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52 ## |
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53 ## used internally in system data structure format manipulations. |
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54 ## @end deftypefn |
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55 |
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56 ## Author: R. Bruce Tenison <btenison@eng.auburn.edu> |
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57 ## Created: June 24, 1994 |
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58 ## a s hodel: modified to allow for pure gain blocks Aug 1996 |
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59 |
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60 function [num, den] = ss2tf (a, b, c, d) |
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61 |
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62 if (nargin != 4) |
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63 print_usage (); |
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64 endif |
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65 |
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66 ## Check args |
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67 [n, m, p] = abcddim (a, b, c, d); |
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68 if (n == -1) |
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69 num = []; |
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70 den = []; |
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71 error("ss2tf: Non compatible matrix arguments"); |
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72 elseif (m != 1 || p != 1) |
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73 num = []; |
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74 den = []; |
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75 error ("ss2tf: not SISO system: m=%d, p=%d", m, p); |
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76 endif |
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77 |
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78 if(n == 0) |
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79 ## gain block only |
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80 num = d; |
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81 den = 1; |
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82 else |
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83 ## First, get the denominator coefficients |
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84 den = poly (a); |
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85 |
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86 ## Get the zeros of the system |
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87 [zz, g] = tzero (a, b, c, d); |
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88 |
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89 ## Form the Numerator (and include the gain) |
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90 if (! isempty (zz)) |
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91 num = g * poly (zz); |
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92 else |
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93 num = g; |
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94 endif |
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95 |
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96 ## the coefficients must be real |
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97 den = real (den); |
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98 num = real (num); |
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99 endif |
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100 |
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101 endfunction |
