1c_csa2xs(3NCARG)                 NCAR GRAPHICS                c_csa2xs(3NCARG)
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NAME

6       c_csa2xs  -  cubic  spline approximation, expanded entry for two-dimen‐
7       sional input, gridded output
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FUNCTION PROTOTYPE

10       float *c_csa2xs(int, float [], float [], float [], float [], int [], float,
11                       int [], int, int, float [], float [], int *);
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SYNOPSIS

16       int c_csa2xs(int ni, float xi[], float yi[], float zi[], float wts[],
17                    int knots[2], float smth, int nderiv[2], int no, int mo,
18                    float xo[], float yo[], int *ier);
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DESCRIPTION

22       ni          (integer,input) The number of input data points. It must be
23                   that  ni  is  greater  than 3 and, depending on the size of
24                   knots below, n may have to be larger.
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26       xi          (real, input) An array dimensioned for ni containing the  X
27                   coordinate values for the input function.
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29       yi          (real,  input) An array dimensioned for ni containing the Y
30                   coordinate values for the input function.
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32       zi          (real, input) An array containing the functional values  of
33                   the  input  function  --  zi[k]  is the functional value at
34                   (xi[k], yi[k]) for k=0,ni-1.
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36       wts         (real, input) An array containing weights for the zi values
37                   at the input xi values, that is, wts[l] is a weight for the
38                   value of zi[l] for l=0,ni-1. If you do not desire to weight
39                   the  input zi values, then set wts[0] to -1. The weights in
40                   the wts array are relative and may be set to any  non-nega‐
41                   tive value. When c_csa2xs is called, the weights are summed
42                   and the individual  weights  are  normalized  so  that  the
43                   weight sum is unity.
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45       knots       (integer,  input)  The  number  of knots to be used in each
46                   coordinate  direction  in  constructing  the  approximation
47                   spline.  knots must be at least 4. The larger the value for
48                   knots, the closer the approximated curve will come to pass‐
49                   ing through the input function values.
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51       smth        (real,  input) A parameter that controls extrapolation into
52                   data sparse regions. If smth is zero, then nothing  special
53                   is  done  in  data  sparse regions. A good first choice for
54                   smth is 1.
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56       nderiv      (real, input) For each of  the  two  coordinate  direction,
57                   specifies  whether  you  want functional values (nderiv=0),
58                   first derivative values (nderiv=1),  or  second  derivative
59                   values   (nderiv=2).   For   example,  if  nderiv[0]=1  and
60                   nderiv[1]=1, then the second order mixed partial  would  be
61                   computed.
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63       no          (integer,  input)  The  number of X coordinate values to be
64                   calculated for the output surface.
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66       mo          (integer, input) The number of Y coordinate  values  to  be
67                   calculated for the output surface.
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69       xo          (real,  input) An array dimensioned for no containing the X
70                   coordinate values for the output grid.
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72       yo          (real, output) An array dimensioned for mo containing the Y
73                   coordinates of the output grid.
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75       ier         (pointer to integer, output) An error return value. If *ier
76                   is returned as 0, then no errors were detected. If *ier  is
77                   non-zero,  then  refer to the error list in the error table
78                   for details.
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USAGE

81       c_csa2xs is called to find an approximating cubic  spline  surface  for
82       two-dimensional  input  data.  c_csa2xs is called if you want to weight
83       the input data values, calculate derivatives,  or  handle  data  sparse
84       areas  specially.   If you do not want to do any of these three things,
85       then use c_csa2s.
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87       c_csa2xs returns a pointer to a  linear  array  of  data  that  is  the
88       approximated  grid  stored  in  row-major  order.  That  is,  if out is
89       declared as
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91         float *out;
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93       and we set:
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95       out = c_csa2xs(ni, xi, yi, zi, wts, knots, smth, nderiv,
96                      no, mo, xo, yo, &ier);
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98       then out[i*mo+j] is the approximated function value at coordinate point
99       (xo[i],  yo[j])  for  0 <= i < no and 0 <= j < mo. The space for out is
100       allocated internal to c_csa2xs and is no * mo floats in size.
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ACCESS

103       To use c_csa2xs, load the NCAR Graphics library ngmath.
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SEE ALSO

106       csagrid, c_csa2s, c_csa2ls, c_csa2lxs
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108       Complete documentation for Csagrid is available at URL
109       http://ngwww.ucar.edu/ngdoc/ng/ngmath/csagrid/csahome.html
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112       Copyright (C) 2000
113       University Corporation for Atmospheric Research
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115       The use of this Software is governed by a License Agreement.
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119UNIX                             January 1999                 c_csa2xs(3NCARG)
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