Init from the patch in the issue 3198
Formatting fixes
Add __init__.py for sympy/calculus
Add examples to docstring
Add references
Add tests
Autodetect funcs and vars
Test euler_equations interface
Get rid of using numbered_symbols, no integration here
Support lagrangians with higher-order derivatives
Test lagragians with high-order derivatives
Refine docstring
initial sphinx docs for calculus module
Issue 3656: Implementation of fancy indexing in matrix
give Sparse an extract method; let Sparse use fancy indices
remove testing for slice in a2idx
edit submatrix doc and copy docs into sparse.py
Bump version to 0.7.4-git
Corrected cross product determinant representation.
Merge pull request #2641 from pestrickland/master

Mechanics documentation correction