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Micro-optimize rotation transform. - #22108

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timhoffm merged 1 commit into
matplotlib:mainfrom
anntzer:fr
Jan 5, 2022
Merged

timhoffm merged 1 commit into
matplotlib:mainfrom
anntzer:fr

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@anntzer

@anntzer anntzer commented Jan 5, 2022

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The following test script shows a ~3x speedup.

import math, numpy as np

mtx = np.array([[.1, .2, .3], [.4, .5, .6], [0, 0, 1]])
theta = np.pi / 4

def rotate(mtx, theta):
    a = math.cos(theta)
    b = math.sin(theta)
    rotate_mtx = np.array([[a, -b, 0.0], [b, a, 0.0], [0.0, 0.0, 1.0]],
                          float)
    return np.dot(rotate_mtx, mtx)

def rfast(mtx, theta):
    a = math.cos(theta)
    b = math.sin(theta)
    (xx, xy, x0), (yx, yy, y0), _ = mtx.tolist()
    # mtx = [[a -b 0], [b a 0], [0 0 1]] * mtx
    mtx[0, 0] = a * xx - b * yx
    mtx[0, 1] = a * xy - b * yy
    mtx[0, 2] = a * x0 - b * y0
    mtx[1, 0] = b * xx + a * yx
    mtx[1, 1] = b * xy + a * yy
    mtx[1, 2] = b * x0 + a * y0
    return mtx

%timeit rotate(mtx, theta)
%timeit rfast(mtx, theta)

PR Summary

PR Checklist

Tests and Styling

  • Has pytest style unit tests (and pytest passes).
  • Is Flake 8 compliant (install flake8-docstrings and run flake8 --docstring-convention=all).

Documentation

  • New features are documented, with examples if plot related.
  • New features have an entry in doc/users/next_whats_new/ (follow instructions in README.rst there).
  • API changes documented in doc/api/next_api_changes/ (follow instructions in README.rst there).
  • Documentation is sphinx and numpydoc compliant (the docs should build without error).

The following test script shows a ~3x speedup.

```python
import math, numpy as np

mtx = np.array([[.1, .2, .3], [.4, .5, .6], [0, 0, 1]])
theta = np.pi / 4

def rotate(mtx, theta):
    a = math.cos(theta)
    b = math.sin(theta)
    rotate_mtx = np.array([[a, -b, 0.0], [b, a, 0.0], [0.0, 0.0, 1.0]],
                          float)
    return np.dot(rotate_mtx, mtx)

def rfast(mtx, theta):
    a = math.cos(theta)
    b = math.sin(theta)
    (xx, xy, x0), (yx, yy, y0), _ = mtx.tolist()
    # mtx = [[a -b 0], [b a 0], [0 0 1]] * mtx
    mtx[0, 0] = a * xx - b * yx
    mtx[0, 1] = a * xy - b * yy
    mtx[0, 2] = a * x0 - b * y0
    mtx[1, 0] = b * xx + a * yx
    mtx[1, 1] = b * xy + a * yy
    mtx[1, 2] = b * x0 + a * y0
    return mtx

%timeit rotate(mtx, theta)
%timeit rfast(mtx, theta)
```

@jklymak jklymak left a comment •

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mtx isn't a pointer, is it?

@anntzer

anntzer commented Jan 5, 2022 •

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It is. (Or rather, modifications are done in place.)

@tacaswell tacaswell added this to the v3.6.0 milestone Jan 5, 2022

@timhoffm timhoffm left a comment •

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@anntzer

Some notes, possibly for follow-ups:

  • skew() could also be rewritten to be element-wise
  • Does it still make sense to keep Affine2D._mtx as a numpy array if we only do element-wise operations?

@timhoffm
timhoffm merged commit 45de25e into matplotlib:main Jan 5, 2022
@anntzer
anntzer deleted the fr branch January 5, 2022 22:44
@anntzer anntzer mentioned this pull request Jan 5, 2022
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4 participants