Some tips about BigFloat

[putianyi889]

I once planned to add this post to documentations, but some of these tips are workarounds for bugs which I have encountered and can be fixed at any time so I decide to put them here.

• Use BigFloat arguments to create BigFloat Spaces and Operators.

• ZeroOperator needs extra type declaration: Use ZeroOperator(BigFloat, dspace, rspace).

• If you want to use IdentityOperator(space), use ConstantOperator(BigFloat(1),space) instead.