Metadata-Version: 2.1
Name: lcapy
Version: 0.33.4
Summary: Symbolic linear circuit analysis
Home-page: https://github.com/mph-/lcapy
Author: Michael Hayes
Author-email: michael.hayes@canterbury.ac.nz
License: UNKNOWN
Download-URL: https://github.com/mph-/lcapy
Platform: UNKNOWN
Classifier: Programming Language :: Python :: 3
Classifier: License :: OSI Approved :: GNU Lesser General Public License v2 or later (LGPLv2+)
Classifier: Operating System :: OS Independent
Description-Content-Type: text/markdown
Requires-Dist: matplotlib
Requires-Dist: scipy
Requires-Dist: numpy
Requires-Dist: sympy

Lcapy is a Python package for linear circuit analysis.  It uses SymPy
for symbolic mathematics.

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Lcapy can analyse circuits described with netlists or by series/parallel combinations of components.

Comprehensive documentation can be found at http://lcapy.elec.canterbury.ac.nz


Circuit analysis
----------------

The circuit is described using netlists, similar to SPICE, with
arbitrary node names (except for the ground node which is labelled 0).
The netlists can be loaded from a file or created at run-time.  For
example:

    >>> from lcapy import Circuit, s
    >>> cct = Circuit("""
    ... Vs 2 0 {5 * u(t)}
    ... Ra 2 1
    ... Rb 1 0
    ... """)

The circuit can then be interrogated to determine branch currents,
branch voltages, and node voltages (with respect to the ground node 0).

    >>> cct[1].v
    >>> cct[2].v
    >>> cct.Ra.i
    >>> cct.Ra.V(s)


One-port networks
-----------------

One-port networks can be created by series and parallel combinations
of other one-port networks.  The primitive one-port networks are the
following ideal components:

- V independent voltage source
- I independent current source
- R resistor
- C capacitor
- L inductor

These components are converted to s-domain models and so capacitor and
inductor components can be specified with initial voltage and
currents, respectively, to model transient responses.

The components have the following attributes:

- Zoc open-circuit impedance
- Ysc short-circuit admittance
- Voc open-circuit voltage
- Isc short-circuit current

The component values can be specified numerically or symbolically
using strings, for example,

    >>> from lcapy import Vdc, R, L, C, s, t
    >>> R1 = R('R_1') 
    >>> L1 = L('L_1')
    >>> a = Vdc(10) + R1 + L1

Here a is the name of the network formed with a 10 V DC voltage source in
series with R1 and L1.

The s-domain open circuit voltage across the network can be printed with:

    >>> a.V(s)
    10/s

The time domain open circuit voltage is given by:

    >>> a.V(t)
    10

The s-domain short circuit current through the network can be printed with:

    >>> a.Isc(s)
    10/(L_1*s**2 + R_1*s)

The time domain short circuit current is given by:

    >>> a.Isc(t)
    10/R_1


Two-port networks
-----------------

One-port networks can be combined to form two-port networks.  Methods
are provided to determine transfer responses between the ports.

Here's an example of creating a voltage divider (L section)

    >>> from lcapy import *
    >>> a = LSection(R('R_1'), R('R_2'))


Limitations
-----------

1. Non-linear components cannot be modelled (apart from a linearisation around a bias point).

2. High order systems can go crazy.

3. Some two-ports generate singular matrices.


Schematics
----------

LaTeX schematics can be generated using circuitikz from the netlist.
Additional drawing hints, such as direction and size are required.

    >>> from lcapy import Circuit
    >>> cct = Circuit("""
    ... P1 1 0; down
    ... R1 1 3; right
    ... L1 3 2; right
    ... C1 3 0_1; down
    ... P2 2 0_2; down
    ... W 0 0_1; right
    ... W 0_1 0_2; right""")
    >>> cct.draw(filename='pic.tex')

In this example, P denotes a port (open-circuit) and W denotes a wire
(short-circuit).  The drawing hints are separated from the netlist
arguments by a semicolon.  They are a comma separated list of
key-value pairs except for directions where the dir keyword is
optional.  The symbol label can be changed using the l keyword; the
voltage and current labels are specified with the v and i keywords.
For example,

    >>> from lcapy import Circuit
    >>> cct = Circuit("""
    ... V1 1 0; down
    ... R1 1 2; left=2, i=I_1, v=V_{R_1}
    ... R2 1 3; right=2, i=I_2, v=V_{R_2}
    ... L1 2 0_1; down, i=I_1, v=V_{L_1}
    ... L2 3 0_3; down, i=I_1, v=V_{L_2}
    ... W 0 0_3; right
    ... W 0 0_1; left""")
    >>> cct.draw(scale=3, filename='pic2.svg')

The drawing direction is with respect to the positive node; i.e., the
drawing is performed from the positive to the negative node.  Since
lower voltages are usually lower in a schematic, then the direction of
voltage sources and ports is usually down.

By default, component (and current) labels are drawn above horizontal
components and to the right of vertical components.  Voltage labels
are drawn below horizontal components and to the left of vertical
components.

Node names containing a dot or underscore are not displayed.


Jupyter Notebooks
-----------------

Lcapy can be used with Jupyter Notebooks (some example notebooks are
in the notebooks directory).  Schematics are drawn inline using png
(svg output is currently disabled due to problems with multiple svg
files sharing the same namespace).  The transient and frequency
response of a circuit can also be drawn inline using the magic command
`%matplotlib`.


Documentation
-------------

For comprehensive documentation, see http://lcapy.elec.canterbury.ac.nz

Alternatively, the documentation can be viewed in a web browser after
running 'make html' in the doc directory.

For another view on Lcapy see https://blog.ouseful.info/2018/08/07/an-easier-approach-to-electrical-circuit-diagram-generation-lcapy/


Testing
-------

The testsuite can be run using

    $ nosetests3 --pdb

Better still, use the --pdb option to enter the Python debugger on a failure:

    $ nosetests3 --pdb

To check for coverage use:

    $ nosetests3 -with-coverage --cover-package=lcapy --cover-html

and then view cover/index.html in a web browser.


Updates
-------

- Version 0.32.3 introduces state-space analysis.  The API is experimental and may change.

- Version 0.32.0 changes the naming of symbolic values.  Previously R1 was converted to R_1 before being converted into a SymPy symbol.  This behaviour was not obvious for symbol substitution.  Now the symbol names are converted on printing.

- Version 0.31.0 reworks schematic drawing.  The syntax for chips has changed since there are no explicit nodes in the netlist.

- Version 0.30.0 tweaks the syntax to perform transformations based on the argument, e.g., V(s) or V(t)

- Version 0.28.0 works with Sympy 1.2.

- Version 0.26.0 adds noise analysis.

- Version 0.25.1 adds time-domain analysis for circuits without reactive
components.

- From version 0.25.0, Lcapy performs more comprehensive circuit
analysis using combinations of DC, AC, and Laplace analysis.  This
added functionality has resulted in a slight change of syntax.
cct.R1.V no longer prints the s-domain expression but the
decomposition of a signal into each of the transform domains.


Copyright 2014--2019 Michael Hayes, UCECE


