From cc717c325f55aebdbdda5a8e344c6adc08c94b3f Mon Sep 17 00:00:00 2001
From: Joseph Weston <joseph@weston.cloud>
Date: Wed, 13 Feb 2019 12:35:06 +0100
Subject: [PATCH] add whatsnew entry for 'System.parameters'
---
doc/source/pre/whatsnew/1.4.rst | 32 ++++++++++++++++++++++++++++++++
1 file changed, 32 insertions(+)
diff --git a/doc/source/pre/whatsnew/1.4.rst b/doc/source/pre/whatsnew/1.4.rst
index 44adfb8d..e29c11af 100644
--- a/doc/source/pre/whatsnew/1.4.rst
+++ b/doc/source/pre/whatsnew/1.4.rst
@@ -138,6 +138,38 @@ the scattering region and leads, one could do the following::
kwant.smatrix(syst, params=dict(V_dot=0, V_lead=1))
+System parameters can now be inspected
+--------------------------------------
+In modern Kwant the preferred way to pass arguments to your models
+is by *name*, using a dictionary and ``params``::
+
+ def onsite(site, magnetic_field, voltage):
+ return magnetic_field * sigma_z + voltage * sigma_0
+
+ def lead_onsite(site, lead_voltage):
+ return lead_voltage * sigma_0
+
+ syst = make_system(onsite)
+ syst.attach_lead(make_lead(lead_onsite))
+ syst = syst.finalized()
+
+ # naming the arguments makes things clear!
+ kwant.smatrix(syst, params=dict(magnetic_field=0.5, voltage=1,
+ lead_voltage=0.2))
+
+This is a much clearer and less error prone than passing arguments by
+*position* using ``args``, as was required in older versions of Kwant.
+In this version of Kwant we introduce the ``parameters`` attribute of
+*finalized systems*, which allows inspection of the names of the
+parameters that the system (and its leads) expects::
+
+ >>> syst.parameters
+ frozenset({'magnetic_field', 'voltage'})
+ >>> syst.leads[0].parameters
+ frozenset({'V_lead'})
+
+This is a provisional API that may be changed in a future version of Kwant.
+
Interpolated density plots
--------------------------
A new function `~kwant.plotter.density` has been added that can be used to
--
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