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Add exponential kernel to Graph #761

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Aug 15, 2024
Merged

Add exponential kernel to Graph #761

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7 changes: 7 additions & 0 deletions libpysal/graph/_kernel.py
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,11 @@ def _cosine(distances, bandwidth):
return (numpy.pi / 4) * numpy.cos(numpy.pi / 2 * u)


def _exponential(distances, bandwidth):
u = distances / bandwidth
return numpy.exp(-u)


def _boxcar(distances, bandwidth):
r = (distances < bandwidth).astype(int)
return r
Expand All @@ -64,6 +69,7 @@ def _identity(distances, _):
"cosine": _cosine,
"boxcar": _boxcar,
"discrete": _boxcar,
"exponential": _exponential,
"identity": _identity,
None: _identity,
}
Expand Down Expand Up @@ -106,6 +112,7 @@ def _kernel(
- gaussian:
- bisquare:
- cosine:
- exponential:
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should these all probably have formulas here?

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Ideally

- boxcar/discrete: all distances less than `bandwidth` are 1, and all
other distances are 0
- identity/None : do nothing, weight similarity based on raw distance
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3 changes: 3 additions & 0 deletions libpysal/graph/tests/test_kernel.py
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Expand Up @@ -224,6 +224,9 @@ def test_kernels(kernel, grocs):
elif kernel in ["identity", None]:
assert weight.mean() == pytest.approx(39758.007361814016)
assert weight.max() == pytest.approx(127937.75271993055)
elif kernel in ["exponential", None]:
assert weight.mean() == pytest.approx(0.25104208195691335)
assert weight.max() == pytest.approx(0.9875261386315732)
else: # function
assert weight.mean() == pytest.approx(0.6880384553732511)
assert weight.max() == pytest.approx(0.9855481738848647)
Expand Down