man c_csa3s (3): 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.

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