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1 ## Copyright (C) 1995, 1996 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, 59 Temple Place - Suite 330, Boston, MA |
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18 ## 02111-1307, USA. |
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19 |
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20 ## -*- texinfo -*- |
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21 ## @deftypefn {Function File} {} pv (@var{r}, @var{n}, @var{p}, @var{l}, @var{method}) |
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22 ## Returns the present value of an investment that will pay off @var{p} for @var{n} |
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23 ## consecutive periods, assuming an interest @var{r}. |
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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 argument @var{method} may be used to specify whether |
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29 ## 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 ## |
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32 ## Note that the rate @var{r} is specified as a fraction (i.e., 0.05, |
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33 ## not 5 percent). |
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34 ## @end deftypefn |
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35 ## |
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36 ## @seealso{pmt, nper, rate, and npv} |
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37 |
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38 ## Author: KH <Kurt.Hornik@ci.tuwien.ac.at> |
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39 ## Description: Present value of an investment |
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40 |
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41 function v = pv (r, n, p, l, m) |
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42 |
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43 if ((nargin < 3) || (nargin > 5)) |
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44 usage ("pv (r, n, p, l, method)"); |
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45 endif |
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46 |
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47 if (! (isscalar (r) && (r > -1))) |
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48 error ("pv: r must be a scalar > -1"); |
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49 elseif (! (isscalar (n) && (n > 0))) |
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50 error ("pv: n must be a positive scalar"); |
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51 elseif (! isscalar (p)) |
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52 error ("pv: p must be a scalar"); |
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53 endif |
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54 |
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55 if (r != 0) |
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56 v = p * (1 - (1 + r)^(-n)) / r; |
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57 else |
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58 v = p * n; |
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59 endif |
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60 |
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61 if (nargin > 3) |
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62 if (nargin == 5) |
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63 if (! isstr (m)) |
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64 error ("pv: `method' must be a string"); |
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65 endif |
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66 elseif (isstr (l)) |
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67 m = l; |
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68 l = 0; |
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69 else |
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70 m = "e"; |
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71 endif |
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72 if (strcmp (m, "b")) |
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73 v = v * (1 + r); |
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74 endif |
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75 if (isscalar (l)) |
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76 v = v + pvl (r, n, l); |
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77 else |
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78 error ("pv: l must be a scalar"); |
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79 endif |
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80 endif |
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81 |
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82 endfunction |
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83 |
