c_csa2lxs - cubic spline approximation, expanded entry for two-dimensional
input, list output
float *c_csa2lxs(int, float [], float [], float [], float [], int [],
float, int [], int, float [], float [], int *);
int c_csa2lxs(int n, float xi[], float yi[], float zi[],
float wts[], int knots[2], float smth, int nderiv[2],
int no, float xo[], float yo[], int *ier);
- n
- (integer, input) The number of input data points. It must
be that n 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 n containing the X
coordinate values for the input function.
- yi
- (real, input) An array dimensioned for n 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,n-1.
- wts
- (real, input) An array containing weights for the zi values
at the input xi and yi values, that is, wts[l] is a weight for the value
of zi[l] for l=0,n-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_csa2lxs 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
constructing the approximation spline. knots[0] and knots[1] 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
- (integer, 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 - Y coordinate values to
be calculated for the output array.
- xo
- (real, input) An array dimensioned for no containing the X
coordinates of the output list.
- yo
- (real, output) An array dimensioned for no containing the Y
coordinates of the output list.
- 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_csa2lxs is called to find values of an approximating cubic spline at specified
two-dimensional coordinates. If you want to weight the input data values,
calculate derivatives, or handle data sparse areas specially, then you will
need to use c_csa2lxs.
c_csa2lxs returns a pointer to a linear array of data that contains the
approximated values calculated at the input list of coordinate values. That
is, if out is declared as
float *out;
and we set:
out = c_csa2lxs(n, x, y, z, wts, knots, smth, nderiv, no, xo, yo, &ier);
then out[i] is the approximated function value at coordinate point (xo[i],
yo[i]) for 0 <= i < no. The space for out is allocated internal to
c_csa2lxs and is no floats in size.
To use c_csa2lxs, load the NCAR Graphics library ngmath.
csagrid, c_csa2s, c_csa2xs, c_csa2ls
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.