Commit b416e486 authored by Christoph Groth's avatar Christoph Groth
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expand whatsnew item about defaults values being no longer allowed

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......@@ -6,8 +6,8 @@ See also the `full list of changes up to the most recent bugfix
release of the 1.4 series
Value functions no longer accept default values for parameters
Value functions may no longer have default values for parameters
Using value functions with default values for parameters can be
problematic, especially when re-using value functions between simulations.
When parameters have default values it is easy to forget that such a
......@@ -35,6 +35,16 @@ Concretely, the above means that the following no longer works::
# Raises ValueError
syst = syst.finalized()
As a solution, simply remove the default values and always provide ``t``.
To deal with many parameters, the following idiom may be useful::
defaults = dict(a=0, b=1, c=2, d=3)
smatrix = kwant.smatrix(syst, E, params=dict(defaults, d=4, e=5))
Note that it allows to override defaults as well as to add additional
System parameter substitution
After the introduction of ``Builder.fill`` it has become possible to construct
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