# Nutils 2 Chuka Men

Nutils 2.0 was released on February 18th, 2016.

## What's New?

These are the main additions and changes since Nutils 1 Bakmi.

### Changed: jump sign

The jump operator has been changed according to the following definition: jump(f) = opposite(f) - f. In words, it represents the value of the argument from the side that the normal is pointing toward, minus the value from the side that the normal is pointing away from. Compared to the old definition this means the sign is flipped.

### Changed: Topology objects

The Topology base class no longer takes a list of elements in its constructor. Instead, the __iter__ method should be implemented by the derived class, as well as __len__ for the number of elements, and getelem(index) to access individual elements. The 'elements' attribute is deprecated.

The nutils.topology.StructuredTopology object no longer accepts an array with elements. Instead, an 'axes' argument is provided with information that allows it to generate elements in the fly. The 'structure' attribute is deprecated. A newly added shape tuple is now a documented attribute.

### Changed: properties dumpdir, outdir, outrootdir

Two global properties have been renamed as follows:

• dumpdir → outdir
• outdir → outrootdir

The outrootdir defaults to ~/public_html and can be redefined from the command line or in the .nutilsrc configuration file. The outdir defaults to the current directory and is redefined by util.run, nesting the name/date/time subdirectory sequence under outrootdir.

### Changed: sum axis argument

The behaviour of nutils.function.sum is inconsistent with that of the Numpy counterparts. In case no axes argument is specified, Numpy sums over all axes, whereas Nutils sums over the last axis. To undo this mistake and transition to Numpy's behaviour, calling sum without an axes argument is deprecated and will be forbidden in Nutils 3.0. In Nutils 4.0 it will be reintroduced with the corrected meaning.

### Changed: strict dimension equality in function.outer

The nutils.function.outer method allows arguments of different dimension by left-padding the smallest prior to multiplication. There is no clear reason for this generality and it hinders error checking. Therefore in future in function.outer(a, b), a.ndim must equal b.ndim. In a brief transition period non-equality emits a warning.

### Changed: Evaluable base class

Relevant only for custom nutils.function.Evaluable objects, the evalf method changes from constructor argument to instance/class method:

class MyEval( function.Evaluable):
def __init__(self, ...):
function.Evaluable(args=[...], shape=...)
def evalf( self, ...):
...


Moreover, the args argument may only contain Evaluable objects. Static information is to be passed through self.

### Removed: _numeric C-extension

At this point Nutils is pure Python. It is no longer necessary to run make to compile extension modules. The numeric.py module remains unchanged.

### Periodic boundary groups

Touching elements of periodic domains are no longer part of the boundary topology. It is still available as boundary of an appropriate non-periodic subtopology:

domain.boundary['left'] # no longer valid
domain[:,:1].boundary['left'] # still valid


### New module: transform

The new nutils.transform module provides objects and operations relating to affine coordinate transformations.

### Traceback explorer disabled by default

The new command line switch --tbexplore activates the traceback explorer on program failure. To change the default behavior add tbexplore=True to your .nutilsrc file.

### Rich output

The new command line switch --richoutput activates color and unicode output. To change the default behavior add richoutput=True to your .nutilsrc file.