Provided by: libncarg-dev_6.3.0-6build1_amd64

**NAME**

c_csa3s - cubic spline approximation, simple entry for three-dimensional input, gridded output

**FUNCTION** **PROTOTYPE**

float *c_csa3s(int, float [], float [], float [], float [], int [], int, int, int, float [], float [], float [], int *);

**SYNOPSIS**

float *c_csa3s (int n, float xi[], float yi[], float zi[], float ui[], int knots[3], int nxo, int nyo, int nzo, float xo[], float yo[], float zo[], int *ier);

**DESCRIPTION**

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 dimensioned for n containing the Z coordinate values for the input function. ui (real, input) An array containing the functional values of the input function -- ui[k] is the functional value at (xi[k], yi[k], zi[k]) for k=0,n-1. knots (integer, input) The number of knots to be used in constructing the approximation spline. knots[0], knots[1] and knots[2] must each be at least 4. The larger the value for knots, the closer the approximated curve will come to passing through the input function values. nxo (integer, input) The number of X coordinate values to be calculated for the output surface. nyo (integer, input) The number of Y coordinate values to be calculated for the output surface. nzo The number of Z coordinate values to be calculated for the output grid. xo (real, input) An array dimensioned for nxo containing the X coordinates of the output grid. yo (real, output) An array dimensioned for nyo containing the Y coordinates of the output grid. zo (real, output) An array dimensioned for nzo containing the Z 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.

**USAGE**

c_csa3s is called to find an approximating cubic spline for three-dimensional input data. If you want to weight the input data values, calculate derivatives, or handle data sparse areas specially, then you will need to use c_csa3xs. c_csa3s returns a pointer to a linear array of data that is the approximation spline stored in row-major order. That is, if out is declared as float *out; and we set: out = c_csa3s(n, x, y, z, u, nx, ny, nz, xo, yo, zo, &ier); then out[nz*ny*i + nz*j + k] is the approximation function value at coordinate point (xo[i], yo[j], zo[k]) for 0 <= i < nx, 0 <= j < ny, and 0 <= k < nz. The space for out is allocated internal to c_csa3s and is nx*ny*nz floats in size.

**ACCESS**

To use c_csa3s, load the NCAR Graphics library ngmath.

**SEE** **ALSO**

csagrid, c_csa3xs, c_csa3ls, c_csa3lxs Complete documentation for Csagrid is available at URL http://ngwww.ucar.edu/ngdoc/ng/ngmath/csagrid/csahome.html

**COPYRIGHT**

Copyright (C) 2000 University Corporation for Atmospheric Research The use of this Software is governed by a License Agreement.