Merge branch 'Sympy_minimal' into 'master'

Bump minimum SymPy version and add Python 3.9 to CI

See merge request !208
9 jobs for release/0.3.0 in 3 minutes and 25 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Test
passed #531733
docker
build-documentation

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passed #531732
docker
flake8-lint

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passed #531726
AVX docker
latest-python

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passed #531729
cuda docker
minimal-conda

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passed #531730
cuda docker
minimal-sympy-master

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passed #531727
win
minimal-windows

00:01:18

manual #531731
AVX cuda11 docker allowed to fail manual
pycodegen-integration
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AVX cuda11 docker
tests-and-coverage

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89.43%
passed #531728
AVX cuda11 docker
ubuntu

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