8000 BUG: Increase accuracy of log1p for small inputs by mfkasim1 · Pull Request #22611 · numpy/numpy · GitHub
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BUG: Increase accuracy of log1p for small inputs #22611

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BUG: Increase accuracy of log1p for small inputs #22611

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3c06dd4
BUG: Increase accuracy of log1p for small inputs
mfkasim1 Nov 17, 2022
c57b5a2
BUG: Handle overflow and underflow for log1p complex
mfkasim1 Nov 18, 2022
59ab5bd
STY: split lines that are too long for log1p complex test
mfkasim1 Nov 18, 2022
efd5c82
TST: Added infj test for log1p complex
mfkasim1 Nov 18, 2022
d559bca
TST: Added decimal arg in testing small numbers
mfkasim1 Nov 18, 2022
c1729cf
TST: Using assert_array_almost_equal_nulp for small numbers
mfkasim1 Nov 18, 2022
3ad9ec3
STY: Put a space after a comma
mfkasim1 Nov 18, 2022
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BUG: Handle overflow and underflow for log1p complex
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@mfkasim1
mfkasim1 committed Nov 18, 2022
commit c57b5a2fecefac096c0bf01fae3a7293f90be621
19 changes: 17 additions & 2 deletions numpy/core/src/umath/funcs.inc.src
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Original file line number Diff line number Diff line change
Expand Up @@ -330,9 +330,24 @@ nc_log1p@c@(@ctype@ *x, @ctype@ *r)
{
@ftype@ xx = x->real;
@ftype@ yy = x->imag;
@ftype@ z = xx * (2 + xx) + yy * yy;
r->imag = npy_atan2@c@(yy, xx + 1);
r->real = 0.5 * npy_log1p@c@(z);

@ftype@ z0 = npy_hypot@c@(xx + 1, yy);

// special case for inputs close to 1
if (z0 < 1.5) {
@ftype@ z = xx * (2 + xx) + yy * yy;
if (z == 0) {
// handle underflow
r->real = xx;
}
else {
r->real = 0.5 * npy_log1p@c@(z);
}
}
else {
r->real = npy_log@c@(z0);
}
return;
}

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12 changes: 11 additions & 1 deletion numpy/core/tests/test_umath.py
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Expand Up @@ -1815,13 +1815,23 @@ def test_log1p_complex(self):
# these numbers are obtained from wolfram alpha
assert_almost_equal(ncu.log1p(1e-18 + 0.1j), 0.00497517 + 0.0996687j)
assert_almost_equal(ncu.log1p(0.1 + 1e-18j), 0.0953102 + 9.09091e-19j)
assert_almost_equal(ncu.log1p(0.5 + 0j), 0.40546510810816 + 0j)
assert_almost_equal(ncu.log1p(0.0 + 0.5j), 0.11157177565710 + 0.46364760900081j)

def test_extreme(self):
# these numbers are obtained from WarrenWeckesser and double checked with wolfram alpha
assert_almost_equal(ncu.log1p(-1 + 1e250j), 575.6462732485114 + 1.5707963267948966j)
assert_almost_equal(ncu.log1p(1e250 + 1j), 575.6462732485114 + 1e-250j)
assert_almost_equal(ncu.log1p(1e250 + 1e250j), 575.9928468387914 + 0.7853981633974483j)
assert_almost_equal(ncu.log1p(1e-250 + 1e250j), 575.6462732485114 + 1.5707963267948966j)
assert_almost_equal(ncu.log1p(1e-250 + 2e-250j), 1e-250 + 2e-250j)
assert_almost_equal(ncu.log1p(1e250 + 1e-250j), 575.6462732485114 + 0.0j)

def test_special(self):
with np.errstate(invalid="ignore", divide="ignore"):
assert_equal(ncu.log1p(np.nan + 1j), np.nan + np.nan * 1j)
assert_equal(ncu.log1p(np.inf + 1j), np.inf + 0j)
assert_equal(ncu.log1p(-np.inf + 1j), np.inf + np.pi * 1j)
assert_equal(ncu.log1p(np.inf * 1j), np.nan + np.nan * 1j)
assert_equal(ncu.log1p(-1 + 0j), -np.inf + 0j)

class TestExpm1:
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