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

6       c_ftsurf - 2D tension spline interpolation of rectangular data
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FUNCTION PROTOTYPE

9       float *c_ftsurf (int, int, float *, float *, float *,
10                        int, int, float *, float *, int *);
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SYNOPSIS

13       float *c_ftsurf (mi, ni, xi, yi, zi, mo, no, xo, yo, ier);
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DESCRIPTION

16       mi          The number of grid lines in the X direction. (mi > 1)
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18       ni          The number of grid lines in the Y direction. (ni > 1)
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20       xi          Pointer  to  an  array  containing m X coordinates for grid
21                   lines in the X direction.
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23       yi          Pointer to an array containing n  Y  coordinates  for  grid
24                   lines in the Y direction.
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26       zi          Pointer  to m x n floats which are the functional values at
27                   the grid points defined by xi and yi.
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29       mo          The number of output values in the X direction.
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31       no          The number of output values in the Y direction.
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33       ier         The value *ier is an error flag as per:
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35                     = 0 -- no error.
36                     = 1 -- if n is less than 2 or m is less than 2.
37                     = 2 -- if X or Y values are not strictly increasing.
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RETURN VALUE

41       c_ftsurf returns a pointer to an array containing mo x no floats  which
42       are  the interpolated values on the grid specified by the arrays xo and
43       yo.
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USAGE

46       This procedure calculates an interpolatory surface  passing  through  a
47       rectangular  grid  of function values. The surface computed is a tensor
48       product of splines under tension.
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50       c_ftsurf is called after all of the desired values for control  parame‐
51       ters  have  been set using the procedures c_ftseti, c_ftsetr, c_ftsetc,
52       c_ftsetfa. The control parameters that apply to c_ftsurf are: sig, zx1,
53       zxm,  zy1,  zyn, z11, zm1, z1n, zmn, df1, df2, df3, df4, df5, df6, df7,
54       df8
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56       The value for the parameter sig specifies the tension  factor.   Values
57       near  zero  result  in a cubic spline; large values (e.g. 50) result in
58       nearly a polygonal line. A typical value is 1. (the default).
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60       zx1 is an array containing n  X-partial  derivatives  of  the  function
61       along  the  line  xi[0],  that is zx1[j] is the X-partial derivative at
62       point (x[0],y[j]) for j=0,n-1. This parameter may be defaulted by  set‐
63       ting  the  value  for  df1 appropriately. The default is to compute zx1
64       internally. Values for zx1 can be set using the procedure c_ftsetfa.
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66       zxm is an array containing n  X-partial  derivatives  of  the  function
67       along  the  line xi[m-1], that is zxm[j] is the X-partial derivative at
68       point (xi[m-1],yi[j]) for j=0,n-1. This parameter may be  defaulted  by
69       setting  the value for df2 appropriately. The default is to compute zx2
70       internally. Values for zxm can be set using the procedure c_ftsetfa.
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72       zy1 is an array containing m  Y-partial  derivatives  of  the  function
73       along  the  line  yi[0],  that is zy1[j] is the Y-partial derivative at
74       point (x[i],y[0]) for i=0,m-1. This parameter may be defaulted by  set‐
75       ting  the  value  for  df3 appropriately. The default is to compute zy1
76       internally. Values for zy1 can be set using the procedure c_ftsetfa.
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78       zyn is an array containing m  Y-partial  derivatives  of  the  function
79       along  the  line yi[n-1], that is zyn[j] is the Y-partial derivative at
80       point (x[i],y[n-1]) for i=0,m-1. This parameter  may  be  defaulted  by
81       setting  the value for df4 appropriately. The default is to compute zyn
82       internally. Values for zyn can be set using the procedure c_ftsetfa.
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84       z11, zm1, z1n, zmn specify X-Y-partial derivatives of the  function  at
85       the   four  corners  (xi[0],yi[0]),  (xi[m-1],yi[0]),  (xi[0],yi[n-1]),
86       (xi[m-1],yi[n-1]), These parameters may be  defaulted  by  setting  the
87       values for df5, df6, df7, df8, appropriately. The default is to compute
88       z11, zm1, z1n, zmn internally.
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ACCESS

91       To use c_ftsurf, load the NCAR Graphics library ngmath.
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SEE ALSO

94       fitgrid_params, c_ftseti, c_ftsetr, c_ftsetc.
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96       Complete documentation for Fitgrid is available at URL
97       http://ngwww.ucar.edu/ngdoc/ng/ngmath/fitgrid/fithome.html
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100       Copyright (C) 2000
101       University Corporation for Atmospheric Research
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103       The use of this Software is governed by a License Agreement.
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107UNIX                              March 1998                  c_ftsurf(3NCARG)
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