CSA1XS(3NCARG)

💖 CSA1XS — the NCAR Graphics one, bestie 💖

okay so. this is a page from the NCAR GRAPHICS manual, and it's all about CSA1XS in section 3NCARG. pull up a chair, grab a strawberry 🍓, and let's get into it.

✨ NAME ✨

CSA1XS — cubic spline approximation, expanded entry for one-dimensional input.

like... it fits a smooth curvy line through your data. but the deluxe version. 💅

🎀 SYNOPSIS 🎀

CALL CSA1XS (NI, XI, YI, WTS, KNOTS, SMTH, DERIV, NO, XO, YO, NWRK,
WORK, IER)

that's the whole call, right there. thirteen things go in / come out. we love a long signature. no cap.

tiny thing i clocked: the synopsis spells it DERIV but the description below spells it NDERIV. just... noting that. 👀

🌸 DESCRIPTION 🌸

here's every single argument, one by one, no skipping, no gatekeeping:

• NI (integer, input) — how many input data points you've got. rules: it must be that NI > 3, and depending on how big KNOTS is (see below), NI might have to be even bigger than that. so, like, don't come in with 3 points. 🙈
• XI (real, input) — an array dimensioned for NI, holding the X coordinates of your input data points.
• YI (real, input) — an array dimensioned for NI, holding the function values at those input XI values. so YI(L) is the value of the input function at XI(L), for L=1,NI. periodt.
• WTS (real, input) — an array dimensioned for NI, holding weights for the YI values at the input XI values. so WTS(L) is a weight for the value of YI(L), for L=1,NI. and bestie, listen: if you do not want to weight the input YI values, just set WTS(1) to -1. that's the move. the weights in WTS are relative, and they can be any non-negative value you like. when CSA1XS gets called, the weights get summed up and then normalized individually so the weight sum is unity. math is doing math. ✨
• KNOTS (integer, input) — the number of knots used to construct the approximation spline. KNOTS must be at least 4. and here's the vibe: the larger your KNOTS, the closer the approximated curve comes to actually passing through the input function values. so crank it if you want that snug fit. 🔥
• SMTH (real, input) — a parameter that controls extrapolation into data sparse regions. if SMTH is zero, then nothing special happens in data sparse regions — it's just business as usual. a good first choice for SMTH is 1. start there, bestie.
• NDERIV (integer, input) — tells it what you actually want back: functional values (NDERIV=0), first derivative values (NDERIV=1), or second derivative values (NDERIV=2). pick your fighter. 👑
• NO (integer, input) — the number of values to be calculated for the output curve.
• XO (real, input) — an array dimensioned for NO, holding the X coordinates of the output curve.
• YO (real, output) — an array dimensioned for NO, holding the calculated function values for the output curve. this is the one that comes out, so it's giving main character energy. 💜
• NWRK (integer, input) — the size of the WORK array. NWRK must be at least KNOTS*(KNOTS+3). do not skimp on the workspace, i'm begging. 😭
• WORK (real, input) — a work array dimensioned for NWRK. it's the backstage crew. essential, unglamorous.
• IER (integer, output) — the error return value. if IER comes back as 0, then no errors were detected — slay. if IER is non-zero, then go read the man page for csagrid_errors for the details. that's your lookup table, not mine.

🦋 USAGE 🦋

CSA1XS gets called when you want to find an approximating cubic spline for one-dimensional input data.

and specifically — you call CSA1XS if you want to do any of these three things:

1. weight the input data values,
2. calculate derivatives, or
3. handle data sparse areas specially.

if you don't want to do any of those three? then just use CSA1S instead. keep it simple, girl. 🌈

⭐ ACCESS ⭐

to use CSA1XS, load the NCAR Graphics library ngmath. that's it. that's the whole access situation.

💀 SEE ALSO 💀

• csagrid
• csa1s
• csa1ls
• csa1lxs

and also! complete documentation for Csagrid lives at this URL, so go be nosy:

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. so like... read it. it's the rules. 🫶

and that's the page!! this one was CSA1XS(3NCARG) from the NCAR GRAPHICS manual, UNIX flavour, dated January 1999. take care of her, go fit some splines, and hydrate. bye bestie 💖✨