# Changelog¶

Nutils is being actively developed and the API is continuously evolving. The following overview lists user facing changes as well as newly added features in inverse chronological order.

## Changes since version 5.0¶

• New command line option: gracefulexit.

The new boolean command line option gracefulexit determines what happens when an exception reaches nutils.cli.run(). If true (default) then the exception is handled as before and a system exit is initiated with an exit code of 2. If false then the exception is reraised as-is. This is useful in particular when combined with an external debugging tool.

• Log tracebacks at debug level.

The way exceptions are handled by nutils.cli.run() is changed from logging the entire exception and traceback as a single error message, to logging the exceptions as errors and tracebacks as debug messages. Additionally, the order of exceptions and traceback is fully reversed, such that the most relevant message is the first thing shown and context follows.

• Solve leniently to relative tolerance in Newton systems.

The nutils.solver.newton method now sets the relative tolerance of the linear system to 1e-3 unless otherwise specified via linrtol. This is mainly useful for iterative solvers which can save computational effort by having their stopping criterion follow the current Newton residual, but it may also help with direct solvers to warn of ill conditioning issues. Iterations furthermore use nutils.matrix.Matrix.solve_leniently(), thus proceeding after warning that tolerances have not been met in the hope that Newton convergence might be attained regardless.

• Linear solver arguments.

The methods nutils.solver.newton, nutils.solver.minimize, nutils.solver.pseudotime, nutils.solver.solve_linear() and nutils.solver.optimize() now receive linear solver arguments as keyword arguments rather than via the solveargs dictionary, which is deprecated. To avoid name clashes with the remaining arguments, argument names must be prefixed by lin.

# deprecated syntax >>> solver.solve_linear(‘lhs’, res, solveargs=dict(solver=’gmres’))

# new syntax >>> solver.solve_linear(‘lhs’, res, linsolver=’gmres’)

• Iterative refinement.

Direct solvers enter an iterative refinement loop in case the first pass did not meet the configured tolerance. In machine precision mode (atol=0, rtol=0) this refinement continues until the residual stagnates.

• Matrix solver tolerances.

The absolute and/or relative tolerance for solutions of a linear system can now be specified in nutils.matrix.Matrix.solve() via the atol resp. rtol arguments, regardless of backend and solver. If the backend returns a solution that violates both tolerances then an exception is raised of type nutils.matrix.ToleranceNotReached, from which the solution can still be obtained via the .best attribute. Alternatively the new method nutils.matrix.Matrix.solve_leniently() always returns a solution while logging a warning if tolerances are not met. In case both tolerances are left at their default value or zero then solvers are instructed to produce a solution to machine precision, with subsequent checks disabled.

• Use stringly for command line parsing.

Nutils now depends on stringly (version 1.0b1) for parsing of command line arguments. The new implementation of nutils.cli.run() is fully backwards compatible, but the preferred method of annotating function arguments is now as demonstrated in all of the examples.

For new Nutils installations Stringly will be installed automatically as a dependency. For existing setups it can be installed manually as follows:

$python3 -m pip install –user –upgrade stringly • Fixed and fallback lengths in (namespace) expressions The nutils.function.Namespace has two new arguments: length_<indices> and fallback_length. The former can be used to assign fixed lengths to specific indices in expressions, say index i should have length 2, which is used for verification and resolving undefined lengths. The latter is used to resolve remaining undefined lengths. >>> ns = nutils.function.Namespace(length_i=2, fallback_length=3) >>> ns.eval_ij('δ_ij') # using length_i Array<2,2> >>> ns.eval_jk('δ_jk') # using fallback_length Array<3,3>  • Treelog update Nutils now depends on treelog version 1.0b5, which brings improved iterators along with other enhancements. For transitional convenience the backwards incompatible changes have been backported in the nutils.log wrapper, which now emits a warning in case the deprecated methods are used. This wrapper is scheduled for deletion prior to the release of version 6.0. To update treelog to the most recent version use: python -m pip install -U treelog  • Unit type The new nutils.types.unit allows for the creation of a unit system for easy specification of physical quantities. Used in conjuction with nutils.cli.run() this facilitates specifying units from the command line, as well as providing a warning mechanism against incompatible units. >>> U = types.unit.create(m=1, s=1, g=1e-3, N='kg*m/s2', Pa='N/m2') >>> def main(length=U('2m'), F=U('5kN')): ... topo, geom = mesh.rectilinear([numpy.linspace(0,length,10)]) $ python myscript.py length=25cm # OK
\$ python myscript.py F=10Pa # error!
• Sample basis

Samples now provide a nutils.sample.Sample.basis(): an array that for any point in the sample evaluates to the unit vector corresponding to its index. This new underpinning of nutils.sample.Sample.asfunction() opens the way for sampled arguments, as demonstrated in the last example below:

>>> H1 = mysample.asfunction(mydata) # mysample.eval(H1) == mydata
>>> H2 = mysample.basis().dot(mydata) # mysample.eval(H2) == mydata
>>> ns.Hbasis = mysample.basis()
>>> H3 = 'Hbasis_n ?d_n' @ ns # mysample.eval(H3, d=mydata) == mydata

• Higher order gmsh geometries

Gmsh element support has been extended to include cubic and quartic meshes in 2D and quadratic meshes in 3D, and parsing the msh file is now a cacheable operation. Additionally, tetrahedra now define bezier points at any order.

• Repository location

The Nutils repository has moved to https://github.com/evalf/nutils.git. For the time being the old address is maintained by Github as an alias, but in the long term you are advised to update your remote as follows:

git remote set-url origin https://github.com/evalf/nutils.git