1 files changed, 22 insertions, 0 deletions
diff --git a/lib/std/math/complex/acos.zig b/lib/std/math/complex/acos.zig
new file mode 100644
index 0000000000..f3526cc9ff
--- /dev/null
+++ b/lib/std/math/complex/acos.zig
@@ -0,0 +1,22 @@
+const std = @import("../../std.zig");
+const testing = std.testing;
+const math = std.math;
+const cmath = math.complex;
+const Complex = cmath.Complex;
+
+/// Returns the arc-cosine of z.
+pub fn acos(z: var) Complex(@typeOf(z.re)) {
+    const T = @typeOf(z.re);
+    const q = cmath.asin(z);
+    return Complex(T).new(T(math.pi) / 2 - q.re, -q.im);
+}
+
+const epsilon = 0.0001;
+
+test "complex.cacos" {
+    const a = Complex(f32).new(5, 3);
+    const c = acos(a);
+
+    testing.expect(math.approxEq(f32, c.re, 0.546975, epsilon));
+    testing.expect(math.approxEq(f32, c.im, -2.452914, epsilon));
+}