ncl_c_csa2lxs man page

c_csa2lxs — cubic spline approximation, expanded entry for two-dimensional input, list output

Function Prototype

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);


(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.
(real, input) An array dimensioned for n containing the X coordinate values for the input function.
(real, input) An array dimensioned for n containing the Y coordinate values for the input function.
(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.
(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.
(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.
(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.
(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.
(integer, input) The number of X - Y coordinate values to be calculated for the output array.
(real, input) An array dimensioned for no containing the X coordinates of the output list.
(real, output) An array dimensioned for no containing the Y coordinates of the output list.
(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.

See Also

csagrid, c_csa2s, c_csa2xs, c_csa2ls

Complete documentation for Csagrid is available at URL


NCAR GRAPHICS January 1999