8000 BUG: npy_acosh fallback too simple. by ewmoore · Pull Request #6976 · numpy/numpy · GitHub
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BUG: npy_acosh fallback too simple. #6976

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Merged
merged 1 commit into from
Jan 8, 2016
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BUG: npy_acosh fallback too simple. #6976

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15 changes: 14 additions & 1 deletion numpy/core/src/npymath/npy_math.c.src
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Original file line number Diff line number Diff line change
Expand Up @@ -221,7 +221,20 @@ double npy_hypot(double x, double y)
#ifndef HAVE_ACOSH
double npy_acosh(double x)
{
return 2*npy_log(npy_sqrt((x + 1.0)/2) + npy_sqrt((x - 1.0)/2));
if (x < 1.0) {
return NPY_NAN;
}

if (npy_isfinite(x)) {
if (x > 1e8) {
return npy_log(x) + NPY_LOGE2;
}
else {
double u = x - 1.0;
return npy_log1p(u + npy_sqrt(2*u + u*u));
}
}
return x;
}
#endif

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