Change isBlade to work on degenerate metrics
#162
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eric-wieser
commented
Oct 22, 2019
clifford/_multivector.py
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| # applying a versor (and hence an invertible blade) to a vector should | ||
| # not change the grade | ||
| if not all( | ||
| grades_present(Vhat*e*Vrev, 0.000001) == {1} | ||
| grade_cmp(grades_present(Vhat*e*Vrev, 0.000001), {1}) | ||
| for e in cf.basis_vectors(self.layout).values() | ||
| ): |
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This condition is relaxed when invertible=False to allow only the removal of grades, but not the addition of any new ones
clifford/_multivector.py
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| # Test if the versor inverse (~V)/(V * ~V) is truly the inverse of the | ||
| # multivector V | ||
| if grades_present(Vhat*Vinv, 0.000001) != {0}: | ||
| if not grade_cmp(grades_present(Vhat*Vinv, 0.000001), {0}): | ||
| return False |
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This condition is relaxed to allow Vhat*Vinv == 0 to be considered
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| mag = (self*Vrev)[()] | ||
| if mag != 0: | ||
| # not strictly necessary, just scales to make eps appropriate below | ||
| Vinv = Vrev / mag | ||
| elif invertible: | ||
| return False | ||
| else: | ||
| Vinv = Vrev |
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Changes here are to:
- bail out early without a divide-by-zero if not allowing non-invertible blades
- avoiding the division if it is zero, since that shouldn't affect the results below significantly
- Use
[()]instead of[0], which is a little more reliable for pulling out the scalar part
eric-wieser
changed the title
isBlade to work on denegerate metricsisBlade to work on degenerate metrics
```python >>> import clifford >>> layout, _ = clifford.Cl(3, 0, 1, firstIdx=0) >>> locals().update(layout.blades) >>> e0.isBlade() True >>> e0.isBlade(invertible=True) False ```
Codecov Report
@@ Coverage Diff @@
## master #162 +/- ##
==========================================
+ Coverage 70.37% 70.43% +0.05%
==========================================
Files 69 69
Lines 9025 9050 +25
Branches 1177 1182 +5
==========================================
+ Hits 6351 6374 +23
- Misses 2507 2508 +1
- Partials 167 168 +1
Continue to review full report at Codecov.
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Fixes #145.
This exposes that
.factorise()and.basis()both fail on non-invertible blades. I'm not sure exactly how to fix that, other than being sure I don't want to do it in this PR.