MAINT: integrate: handle b < a in quad #8336
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scipy/integrate/quadpack.py
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| @@ -330,9 +330,15 @@ def quad(func, a, b, args=(), full_output=0, epsabs=1.49e-8, epsrel=1.49e-8, | |||
| (0.0, 0.0) | |||
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| """ | |||
| if b < a: | |||
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How about:
a, b = min(a, b), max(a, b)
instead of adding this clause?
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Not quite, because below it integrates either f(x) or -f(x), depending on whether a<b or not.
scipy/integrate/quadpack.py
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| @@ -330,9 +330,15 @@ def quad(func, a, b, args=(), full_output=0, epsabs=1.49e-8, epsrel=1.49e-8, | |||
| (0.0, 0.0) | |||
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| """ | |||
| if b < a: | |||
| return quad(lambda x, *args: -func(x, *args), b, a, args, full_output, | |||
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Don't change the integrand function to a lambda (what if the input function is a LowLevelCallable?). Instead, swap the sign of the result.
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Updated. No more wrapping of integrand into a lambda, so a LowLevelCallable passes through without extra overhead. |
scipy/integrate/quadpack.py
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| @@ -332,13 +332,22 @@ def quad(func, a, b, args=(), full_output=0, epsabs=1.49e-8, epsrel=1.49e-8, | |||
| """ | |||
| if not isinstance(args, tuple): | |||
| args = (args,) | |||
| if (weight is None): | |||
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| flip = False | |||
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flip, a, b = b < a, min(a, b), max(a, b)
| retval = _quad(func, a, b, args, full_output, epsabs, epsrel, limit, | ||
| points) | ||
| else: | ||
| retval = _quad_weight(func, a, b, args, full_output, epsabs, epsrel, | ||
| limlst, limit, maxp1, weight, wvar, wopts) | ||
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| if flip: | ||
| retval = (-retval[0],) + retval[1:] |
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I started looking through stats.quadpack._quad to check this line - eek, no docstring saying what it accepts, and what the return values are. Definitely a case for a documentation effort at a future point in time.
EDIT: I was being dense, I understand what this line is doing, but _quad could probably do with more doco.
closes gh-7968