Added identity matrix support (still needs codegen support)

  Added lerp as an overloaded function

  Added type labels to nodes in the differentiation iterator so that the intermediate
  variables get the right type

  Overhaul in the way that the MidIL and LowIL represent tensor types (especially
  for orders > 1).  We still need to deal with the flattening of tensor-value
  construction

  Adding support for vector normalize

  Added FIXME comments for flattening tensors

  Added mechanism for supporting "black box" functions (e.g., sin and sqrt).
  Also added atan2, sqrt, and tan functions to Basis

  Added trace operator for 2x2, 3x3, and 4x4 matrices

  Bug fix: use consistent axis order

  Started to add field normalization code to high-opt

  Bug fix: flip order of components in coefficient vectors so that they match the
  order of the voxel vectors

  Fix coefficients in probe code

  Adding support for initially to IL.  Also factored out more common code from
  high-to-mid and mid-to-low into translate-fn.sml

  Fixed bug in computing coefficients for probes

  Fix bug in order of axes when doing the convolution reduction (should be
  fastest to slowest).

  Fix typo in comment

  Streamlined code for real to int conversions

  Lots of changes to push image info through to the code generator.

  Add border parameter to Inside operator and swap argument order to match
  surface language operator.

  More work on code generation.  Made sure that the census info is initialized for
  all ILs.

  Many changes to IL operators for fields and images.

  Made cfg type immutable

  Change "actor" to "strand"

  Working on porting to new IL

  Creating a branch to explore a pure CFG IL

  Change name of MidIL Transform operator to PosToImgSpace.  Also added GradToWorldSpace operator to MidIL.

  Upated URL in header to diderot-language.cs.uchicago.edu

  Bug fix: get type of Select right

  Adding MidIL checking

  Added more type info to HighIL operators to aid checking.

  bug fixes

  Added types to IL variables

  Moving IL types out of the Op structures into their own per-IL structures.

  Move MidIL types into their own module

  Copy some of the translation boilerplate from the high-to-mid translation
  into the mid-to-low translation

  Debugging probe.sml.

  Added fld2d' test case

  Added HighIL to MidIL translation phase

  Working on translation

  Working on high to mid translation

  Working on high to mid translation

  Debugging generation of probe code

  Debugging probe.sml

  Working on test driver for probe code

  working on HighIL to MidIL translation

  Working on high to mid translation

  Working on HighIL to MidIL translation

  Working on probe code generation

  Working on compiler

  New directory