1c_ftkurvpd(3NCARG)               NCAR GRAPHICS              c_ftkurvpd(3NCARG)
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NAME

6       c_ftkurvpd  - interpolation and derivative calculation for closed para‐
7       metric curves
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FUNCTION PROTOTYPE

10       int c_ftkurvpd (int, float [], float [], int, float [],
11                       float [], float [], float [], float [],
12                       float [], float []);
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SYNOPSIS

15       int c_ftkurvpd (n, xi, yi, m, t, xo, yo, xd, yd, xdd, ydd);
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DESCRIPTION

18       n           The number of input data points. (n > 1)
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20       xi          An array containing the abscissae for the input function.
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22       yi          An array containing the  functional  values  (y[k]  is  the
23                   functional value at x[k] for k=0,n).
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25       m           The number of desired interpolated points.
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27       t           Contains  an array of values for the parameter mapping onto
28                   the interpolated curve. Any interval [tt,tt+1.]  maps  onto
29                   the entire curve.
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31       xo          An  array  containing  the  X  values  for the interpolated
32                   points.  t[k] maps to (xo[k],yo[k]) for k=0,n-1.
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34       yo          An array containing  the  Y  values  for  the  interpolated
35                   points.
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37       xd          Contains  the  first  derivatives  of  the X component with
38                   respect to t.
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40       yd          Contains the first derivatives  of  the  Y  component  with
41                   respect to t.
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43       xdd         Contains  the  second  derivatives  of the X component with
44                   respect to t.
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46       ydd         Contains the second derivatives of  the  Y  component  with
47                   respect to t.
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RETURN VALUE

50       c_ftkurvpd returns an error value as per:
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52       = 0 -- no error.
53       = 1 -- if n is less than 2.
54       = 2 -- if adjacent coordinate pairs coincide.
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USAGE

57       This  procedure behaves like ftkurvp except that in addition it returns
58       the first and second derivatives of  the  component  functions  in  the
59       parameterization.
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61       Given  a  sequence  of  distinct  input  points  (  (x[0],y[0]),  ... ,
62       (x[n-1],y[n-1]), the interpolated curve  is  parameterized  by  mapping
63       points in the interval [0.,1.] onto the interpolated curve. The result‐
64       ing curve has a parametric representation both of whose components  are
65       splines  under  tension  and functions of the polygonal arc length. The
66       value 0. is mapped onto (x[0],y[0]) and the value  1.  is  mapped  onto
67       (x[0],y[0]) as well (completing the closed curve).
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69       c_ftkurvpd is called after all of the desired values for control param‐
70       eters have been set using the procedures c_ftseti, c_ftsetr,  c_ftsetc.
71       The only control parameter that applies to c_ftkurvpd is: sig.
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73       The  value  for  the parameter sig specifies the tension factor. Values
74       near zero result in a cubic spline; large values (e.g.  50)  result  in
75       nearly a polygonal line. A typical value is 1. (the default).
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ACCESS

78       To use c_ftkurvpd, load the NCAR Graphics library ngmath.
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SEE ALSO

81       fitgrid_params, c_ftseti, c_ftsetr, c_ftsetc.
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83       Complete documentation for Fitgrid is available at URL
84       http://ngwww.ucar.edu/ngdoc/ng/ngmath/fitgrid/fithome.html
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87       Copyright (C) 2000
88       University Corporation for Atmospheric Research
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90       The use of this Software is governed by a License Agreement.
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94UNIX                              March 1998                c_ftkurvpd(3NCARG)
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