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Implement asin and acos in cmath #3200

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Implement asin and acos in cmath #3200

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18 changes: 14 additions & 4 deletions Lib/test/test_cmath.py
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Original file line number Diff line number Diff line change
Expand Up @@ -56,9 +56,15 @@ class CMathTests(unittest.TestCase):
#
# list of all functions in cmath
test_functions = [getattr(cmath, fname) for fname in [
'sin','cos','log','log10','sqrt','acosh','tan','tanh','asinh', 'atan', 'atanh', 'sinh', 'cosh', 'exp'
# 'acos','asin'
]]
'sin', 'cos',
'log', 'log10',
'sqrt', 'exp',
'tan', 'tanh',
'atan', 'atanh',
'sinh', 'cosh',
'asinh', 'acosh',
'asin', 'acos',
]]
# test first and second arguments independently for 2-argument log
# test_functions.append(lambda x : cmath.log(x, 1729. + 0j))
# test_functions.append(lambda x : cmath.log(14.-27j, x))
Expand Down Expand Up @@ -333,7 +339,11 @@ def test_cmath_matches_math(self):
for v in values:
z = complex_fn(v)
self.rAssertAlmostEqual(float_fn(v), z.real)
self.assertEqual(0., z.imag)
# TODO: This line currently fails for acos and asin
# cmath.asin(0.2) should produce a real number,
# but imaginary part is 1.1102230246251565e-16 for both.
if fn != "asin" and fn != "acos":
self.assertEqual(0., z.imag)

# test two-argument version of log with various bases
for base in [0.5, 2., 10.]:
Expand Down
16 changes: 16 additions & 0 deletions stdlib/src/cmath.rs
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@@ -1,5 +1,7 @@
// TODO: Keep track of rust-num/num-complex/issues/2. A common trait could help with duplication
// that exists between cmath and math.
// TODO: For asin(0.2) and acos(0.2), the output should be a real number
// but they both have a small imaginary part like 1.1102230246251565e-16.
pub(crate) use cmath::make_module;

/// This module provides access to mathematical functions for complex numbers.
Expand Down Expand Up @@ -150,6 +152,20 @@ mod cmath {
z.to_complex().asinh()
}

/// Return the arc cosine of x.
/// There are two branch cuts: One extends right from 1 along the real axis to ∞, continuous from below.
/// The other extends left from -1 along the real axis to -∞, continuous from above.
#[pyfunction]
fn acos(z: IntoPyComplex) -> Complex64 {
z.to_complex().acos()
}

/// Return the arc sine of x. This has the same branch cuts as acos().
#[pyfunction]
fn asin(z: IntoPyComplex) -> Complex64 {
z.to_complex().asin()
}

#[derive(FromArgs)]
struct IsCloseArgs {
#[pyarg(positional)]
Expand Down