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1 ## Copyright (C) 1995, 1996, 1997 Kurt Hornik |
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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 2, or (at your option) |
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8 ## 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, write to the Free |
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17 ## Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA |
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18 ## 02110-1301, USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {} rate (@var{n}, @var{p}, @var{v}, @var{l}, @var{method}) |
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22 ## Return the rate of return on an investment of present value @var{v} which |
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23 ## pays @var{p} in @var{n} consecutive periods. |
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24 ## |
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25 ## The optional argument @var{l} may be used to specify an additional |
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26 ## lump-sum payment made at the end of @var{n} periods. |
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27 ## |
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28 ## The optional string argument @var{method} may be used to specify |
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29 ## whether payments are made at the end (@code{"e"}, default) or at the |
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30 ## beginning (@code{"b"}) of each period. |
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31 ## @seealso{pv, pmt, nper, npv} |
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32 ## @end deftypefn |
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33 |
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34 ## Author: KH <Kurt.Hornik@wu-wien.ac.at> |
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35 ## Description: Rate of return of an investment |
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36 |
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37 function r = rate (n, p, v, l, m) |
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38 |
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39 if ((nargin < 3) || (nargin > 5)) |
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40 usage ("rate (n, p, v, l, method)"); |
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41 endif |
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42 |
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43 if (! (isscalar (n) && (n > 0))) |
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44 error ("rate: n must be a positive scalar"); |
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45 elseif (! isscalar (p)) |
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46 error ("rate: p must be a scalar"); |
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47 elseif (! isscalar (v)) |
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48 error ("rate: p must be a scalar"); |
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49 endif |
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50 |
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51 if (nargin == 5) |
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52 if (! ischar (m)) |
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53 error ("rate: `method' must be a string"); |
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54 endif |
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55 elseif (nargin == 4) |
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56 if (ischar (l)) |
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57 m = l; |
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58 l = 0; |
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59 else |
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60 m = "e"; |
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61 endif |
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62 else |
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63 l = 0; |
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64 m = "e"; |
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65 endif |
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66 |
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67 if (! isscalar (l)) |
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68 error ("rate: l must be a scalar"); |
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69 endif |
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70 |
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71 [r, info] = fsolve (sprintf ("pv (x, %g, %g, %g, \"%s\") - %g", |
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72 n, p, l, m, v), 0); |
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73 |
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74 endfunction |
