Add pseudo-inverse of tensors and enable tranpose for Vec{dim}

[yijiangh]

Summary

1. Enable tranpose for first-order tensor
2. Add pseudo-inverse for Vec{dim}, Tensor{2,dim}, SymmetricTensor{2, dim}, Tensor{4, dim}, SymmetricTensor{4, dim, T}.

• In the Vec{dim} case, pinv produces Transpose{T, Vec{dim, T}}(t / norm(t))
• In the last four cases, pinv is reduced to inv.

One example use case for pinv of tensors is the elastic simulation of 3D trusses. In a truss element, the reference domain \xi is 1D and the nodal coordinate x is in 3D. Here, dx/d\xi is not a square matrix so it's not invertible. Then, pinv needs to be used.

What type of change is this?

• Bug fix in a backwards-compatible manner.
• New feature in a backwards-compatible manner.
• Breaking change: bug fix or new feature that involve incompatible API changes.
• Other (e.g. doc update, configuration, etc)

Checklist

• I ran all tests on my computer and it's all green (i.e. ] test).
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if appropriate)

[codecov-commenter]

Codecov Report

Merging #139 into master will decrease coverage by 0.84%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #139      +/-   ##
==========================================
- Coverage   95.77%   94.93%   -0.85%     
==========================================
  Files          16       16              
  Lines        1135     1144       +9     
==========================================
- Hits         1087     1086       -1     
- Misses         48       58      +10     

Impacted Files	Coverage Δ
src/Tensors.jl	82.05% <ø> (ø)
src/math_ops.jl	88.23% <0.00%> (-9.60%)	⬇️
src/tensor_ops_errors.jl	100.00% <ø> (ø)

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[codecov-io]

Codecov Report

Merging #139 into master will decrease coverage by 0.84%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #139      +/-   ##
==========================================
- Coverage   95.77%   94.93%   -0.85%     
==========================================
  Files          16       16              
  Lines        1135     1144       +9     
==========================================
- Hits         1087     1086       -1     
- Misses         48       58      +10     

Impacted Files	Coverage Δ
src/Tensors.jl	82.05% <ø> (ø)
src/math_ops.jl	88.23% <0.00%> (-9.60%)	⬇️
src/tensor_ops_errors.jl	100.00% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2af6821...263b064. Read the comment docs.