csqrt(3)

💅 csqrt — complex square root, but make it cute

okay bestie so like. the manual name is csqrt and she is the math girlie for square roots, but for complex numbers ✨. her whole friend group is csqrt, csqrtf, and csqrtl 🫶

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🌈 LIBRARY

Math library (libm, link it with -lm) — yes you have to actually link it, no cap. 🎀

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✨ SYNOPSIS

#include <complex.h>

double complex csqrt(double complex z);
float complex csqrtf(float complex z);
long double complex csqrtl(long double complex z);

like. three of them. same vibe, different precision 🦋

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💖 DESCRIPTION

so these functions find the complex square root of z. iconic behaviour, honestly. 🔥

but here's the tea ☕ — there's a branch cut running along the negative real axis. and the way that works is:

• csqrt(-1+eps*I) is gonna land close to I
• csqrt(-1-eps*I) is gonna land close to -I

…as long as eps is a small positive real number. so like, you approach that negative real axis from above → you get one answer. from below → you get the other one. the discontinuity is just there, and she's not sorry 💅 that's the math, periodt.

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🌸 ATTRIBUTES

ngl if you don't know what these words mean, go read attributes(7) — it's giving required reading 📚

• csqrt(), csqrtf(), csqrtl() — Thread safety: MT-Safe 👑 — so you can call her from multiple threads and she will not have a meltdown. obsessed.

(the original had a whole cute little table for this. this is the table. it's one row. she ate. 🍓)

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⭐ STANDARDS

C11, POSIX.1-2008. certified and official bestie 💜

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🧚 HISTORY

• glibc 2.1 — that's when she first showed up on the scene ✨
• And she's been around since C99 and POSIX.1-2001, so like, a legacy icon fr fr 🌟

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🎀 SEE ALSO

go hang out with her friends:

• cabs(3)
• cexp(3)
• complex(7)

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lowkey reminder: that branch cut is not a bug, it's a feature. don't come for her. 🫶

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csqrt(3) comes to you from Linux man-pages 6.20, dated 2026-02-08 — mwah, love that for her, that's the whole page bestie, go compute something slay 💅💖✨