c_csa2xs - cubic spline approximation, expanded entry for
two-dimensional input, gridded output
float *c_csa2xs(int, float [], float [], float [], float [], int [], float,
int [], int, int, float [], float [], int *);
int c_csa2xs(int ni, float xi[], float yi[], float zi[], float wts[],
int knots[2], float smth, int nderiv[2], int no, int mo,
float xo[], float yo[], int *ier);
- ni
- (integer,input) The number of input data points. It must be that ni is
greater than 3 and, depending on the size of knots below, n may have to be
larger.
- xi
- (real, input) An array dimensioned for ni containing the X coordinate
values for the input function.
- yi
- (real, input) An array dimensioned for ni containing the Y coordinate
values for the input function.
- zi
- (real, input) An array containing the functional values of the input
function -- zi[k] is the functional value at (xi[k], yi[k]) for
k=0,ni-1.
- wts
- (real, input) An array containing weights for the zi values at the input
xi values, that is, wts[l] is a weight for the value of zi[l] for
l=0,ni-1. If you do not desire to weight the input zi values, then set
wts[0] to -1. The weights in the wts array are relative and may be set to
any non-negative value. When c_csa2xs is called, the weights are summed
and the individual weights are normalized so that the weight sum is
unity.
- knots
- (integer, input) The number of knots to be used in each coordinate
direction in constructing the approximation spline. knots must be at least
4. The larger the value for knots, the closer the approximated curve will
come to passing through the input function values.
- smth
- (real, input) A parameter that controls extrapolation into data sparse
regions. If smth is zero, then nothing special is done in data sparse
regions. A good first choice for smth is 1.
- nderiv
- (real, input) For each of the two coordinate direction, specifies whether
you want functional values (nderiv=0), first derivative values (nderiv=1),
or second derivative values (nderiv=2). For example, if nderiv[0]=1 and
nderiv[1]=1, then the second order mixed partial would be computed.
- no
- (integer, input) The number of X coordinate values to be calculated for
the output surface.
- mo
- (integer, input) The number of Y coordinate values to be calculated for
the output surface.
- xo
- (real, input) An array dimensioned for no containing the X coordinate
values for the output grid.
- yo
- (real, output) An array dimensioned for mo containing the Y coordinates of
the output grid.
- ier
- (pointer to integer, output) An error return value. If *ier is returned as
0, then no errors were detected. If *ier is non-zero, then refer to the
error list in the error table for details.
c_csa2xs is called to find an approximating cubic spline surface
for two-dimensional input data. c_csa2xs is called if you want to weight the
input data values, calculate derivatives, or handle data sparse areas
specially. If you do not want to do any of these three things, then use
c_csa2s.
c_csa2xs returns a pointer to a linear array of data that is the
approximated grid stored in row-major order. That is, if out is declared
as
float *out;
and we set:
out = c_csa2xs(ni, xi, yi, zi, wts, knots, smth, nderiv,
no, mo, xo, yo, &ier);
then out[i*mo+j] is the approximated function value at coordinate
point (xo[i], yo[j]) for 0 <= i < no and 0 <= j < mo. The space
for out is allocated internal to c_csa2xs and is no * mo floats in size.
To use c_csa2xs, load the NCAR Graphics library ngmath.
csagrid, c_csa2s, c_csa2ls, c_csa2lxs
Complete documentation for Csagrid is available at URL
http://ngwww.ucar.edu/ngdoc/ng/ngmath/csagrid/csahome.html
Copyright (C) 2000
University Corporation for Atmospheric Research
The use of this Software is governed by a License Agreement.