c_csa3s(3NCARG)

💖 c_csa3s — NAME 💖

okay so bestie, welcome to the NCAR GRAPHICS manual, page c_csa3s(3NCARG). this one is literally "cubic spline approximation, simple entry for three-dimensional input, gridded output" 🦋 and yes that is a whole mouthful, i know.

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🌸 FUNCTION PROTOTYPE 🌸

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

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✨ 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);

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🎀 DESCRIPTION 🎀

• n — (integer, input) the number of input data points, bestie. and listen: it must be that n is greater than 3, and depending on the size of knots below, n may have to be larger. so like, no skimping on data points. 💅
• xi — (real, input) an array dimensioned for n holding the X coordinate values for the input function.
• yi — (real, input) an array dimensioned for n holding the Y coordinate values for the input function.
• zi — (real, input) an array dimensioned for n holding the Z coordinate values for the input function.
• ui — (real, input) an array holding the functional values of the input function — so like, ui[k] is the functional value at (xi[k], yi[k], zi[k]) for k=0,n-1. that's the vibe.
• 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. more knots = more clingy, fr fr.
• 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 comes back as 0, then no errors were detected, slay. if *ier is non-zero, then bestie you gotta refer to the error list in the error table for details. 😭

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🫶 USAGE 🫶

c_csa3s is called to find an approximating cubic spline for three-dimensional input data. but heads up: 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 instead. this one is the simple entry, she's not doing all that.

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. no cap, that's the indexing. and the space for out is allocated internal to c_csa3s and is nx*ny*nz floats in size — so don't go freeing it like it's yours, she made it. 👑

⚠️ that index math is literally the whole game. get it wrong and your surface is giving chaos, not data. 🌀

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🌈 ACCESS 🌈

to use c_csa3s, load the NCAR Graphics library ngmath. that's it, that's the step. ✨

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💜 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 — go read it, iykyk 🧚

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👑 COPYRIGHT 👑

copyright (C) 2000 University Corporation for Atmospheric Research

the use of this Software is governed by a License Agreement.

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and that's the whole page bestie!! this was the UNIX flavor of the c_csa3s(3NCARG) page, dated January 1999, and it came to you straight from the NCAR Graphics crew. mwah. 💅💖🦋