c_csa2lxs(3NCARG)

✨ c_csa2lxs ✨ — bestie edition 💖

okay so this is a page from the NCAR GRAPHICS manual (the 3NCARG corner of the library, iykyk) and it's all about c_csa2lxs, which is literally the expanded entry for cubic spline approximation with two-dimensional input and list output. she's giving ✨math girlie✨ and she's SO good at what she does.

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🌸 NAME 🌸

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

no cap, that's the whole vibe: you hand her a pile of 2D data points, she hands you back a smooth spline approximation. 🎀

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🦋 FUNCTION PROTOTYPE 🦋

float *c_csa2lxs(int, float [], float [], float [], float [], int [],
                 float, int [], int, float [], float [], int *);

look at her. iconic signature. 💅

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⭐ SYNOPSIS ⭐

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);

that's the whole call, bestie. eleven-ish arguments and every single one matters. let's get into it 🫶

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💜 DESCRIPTION 💜

• n — (integer, input) how many input data points you're bringing to the party. IMPORTANT: n has to be greater than 3, and depending on how big knots is (see below) you might need n to be even bigger than that. don't skip this, she will notice. 😭
• xi — (real, input) an array dimensioned for n holding the X coordinate values for your input function. 📍
• yi — (real, input) an array dimensioned for n holding the Y coordinate values for your input function. 📍
• zi — (real, input) an array with the functional values of the input function — so zi[k] is the functional value at (xi[k], yi[k]) for k=0,n-1. that's the tea. 🍓
• wts — (real, input) an array of weights for the zi values at the input xi and yi values, meaning wts[l] is a weight for the value of zi[l] for l=0,n-1. if you don't wanna weight the input zi values, just set wts[0] to -1. the weights in wts are relative and can be any non-negative value. when c_csa2lxs gets called, the weights get summed up and each individual weight is normalized so that the weight sum is unity. so like, she does the math for you, periodt. ⚖️
• knots — (integer, input) how many knots to use when constructing the approximation spline. knots[0] and knots[1] must be at least 4. the bigger the value for knots, the closer the approximated curve gets to passing right through the input function values. more knots = more snuggle with your data. 🔥
• smth — (real, input) a parameter that controls extrapolation into data sparse regions. if smth is zero, then nothing special happens in data sparse regions. a good first choice for smth is 1. 🌫️
• nderiv — (integer, input) for each of the two coordinate directions, this says 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. calculus o'clock, bestie. 📈
• 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. yes bestie, this one is output, don't @ me. 📍
• ier — (pointer to integer, output) the error return value. if *ier comes back as 0, then no errors were detected — we love a clean run. 💖 if *ier is non-zero, then go check the error list in the error table for the details. 🙈

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🎀 USAGE 🎀

you call c_csa2lxs when you wanna find values of an approximating cubic spline at specific two-dimensional coordinates. and lowkey, if you want to weight the input data values, calculate derivatives, or handle data sparse areas specially, then c_csa2lxs is the one you need. she's the main character for a reason. 👑

c_csa2lxs returns a pointer to a linear array of data containing the approximated values calculated at the input list of coordinate values. so, 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. she brings her own memory, we stan a self-sufficient queen. 💅

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🌈 ACCESS 🌈

to use c_csa2lxs, load the NCAR Graphics library ngmath. 🧚

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👑 SEE ALSO 👑

• 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

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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 lil drop of wisdom came out of the UNIX manual, January 1999 edition, from the NCAR GRAPHICS crew — go forth and spline responsibly 🫶🎀💜