c_csa2s(3NCARG)

✨ c_csa2s — the NCAR GRAPHICS bestie ✨

okay so real talk, this is a page from the NCAR GRAPHICS manuals, and today we're doing c_csa2s(3NCARG) 💖

---

💅 NAME 💅

c_csa2s — cubic spline approximation, simple entry for two-dimensional input, gridded output 🦋

like... it fits a smooth cubic spline surface through your scattered 2D points and hands you back a grid. simple entry, gridded output, no cap.

---

🌸 FUNCTION PROTOTYPE 🌸

float *c_csa2s(int, float [], float [], float [], int [],
               int, int, float [], float [], int *);

---

🎀 SYNOPSIS 🎀

int c_csa2s(int n, float xi[], float yi[], float zi[], int knots[2],
            int no, int mo, float xo[], float yo[], int *ier);

---

✨ DESCRIPTION ✨

okay bestie, let's meet the whole cast 🫶

• 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. so like, more than 3 minimum, but honestly check your knots first 👑
• 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 containing the functional values of the input function — zi[k] is the functional value at (xi[k], yi[k]) for k=0,n-1. yes, exactly that indexing, don't fight it 💜
• knots — (integer, input) the number of knots to be used in each coordinate direction 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. so bigger knots = snugger fit, periodt 🔥
• no — (integer, input) the number of X coordinate values to be calculated for the output surface.
• mo — (integer, input) the number of Y coordinate values to be calculated for the output surface.
• xo — (real, input) an array dimensioned for no containing the X coordinates of the output grid.
• yo — (real, output) an array dimensioned for mo containing the Y coordinates of the output grid. (yes bestie, it says output here, we are reading it exactly as written, no notes 🙈)
• ier — (pointer to integer, output) an error return value. if *ier comes back as 0, then no errors were detected. if *ier is non-zero, then go look at the error list in the error table for the deets. lowkey always check it 💀

---

🌈 USAGE 🌈

so you call c_csa2s when you want to find an approximating cubic spline surface for two-dimensional input data. it's giving "I just want the surface, please" ✨

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_csa2xs instead. c_csa2s is the simple entry — it's not doing all that, and that's on purpose 💅

here's the cute part. c_csa2s returns a pointer to a linear array of data that is the approximated grid stored in row-major order. that is, if out is declared as

float *out;

and we set:

out = c_csa2s(n, x, y, z, knots, no, mo, xo, yo, &ier);

then out[i*mo+j] is the approximated function value at coordinate point (xo[i], yo[j]) for 0 <= i < no and 0 <= j < mo. 📐

the space for out is allocated internal to c_csa2s and is no * mo floats in size. iconic allocation behaviour, we love to see it 👑

---

🧚 ACCESS 🧚

to use c_csa2s, load the NCAR Graphics library ngmath.

that's it. that's the whole vibe check. 🌸

---

🦋 SEE ALSO 🦋

• csagrid
• c_csa2xs
• c_csa2ls
• c_csa2lxs

complete documentation for Csagrid is available at URL http://ngwww.ucar.edu/ngdoc/ng/ngmath/csagrid/csahome.html — go read it, it's the source material fr fr 💖

---

👑 COPYRIGHT 👑

Copyright (C) 2000 University Corporation for Atmospheric Research

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

---

and that's the whole page bestie!! 💜 this one shipped as part of the NCAR GRAPHICS manual, dated January 1999, and you'll find it filed under the manual name c_csa2s(3NCARG) on a good old UNIX system. go make some surfaces, you've got this 🎀✨🫶