Matplotlib drawer backend (#352)

* Adding tutorials directory

* test

* BV Algorithm

* add Matplotlib circuit drawer backend, this version works for H, CNOT, and Multi-CNOT.

* Delete the added unnecessary attributes in Command object

* Create the CircuitDrawerMatplotlib Class to handles drawing with matplotlib

* Deleted tutorials/.gitkeep

* update

* fix measurement gate

* Delete unrelated files.

* fix Toffoli gate position issue and change the qubit position from 'str' to 'int'

* Pytest for drawer_mpl

* Tests for _plot function

* Fix the R(angle) gate drawing

* added test for is_available and QFT gate

* fix drawing distance between gates when gate_length >2

* new test png for pytest mpl

* added Swap gates and CSwap gate with multi-control and multi-target.

* update test and comments

* Address comments in _drawer.py

* Reindent and reformat parts of _drawer.py

* Address comments in _plot.py

- Minor tweaks, code cleanup, rewrites, etc.

* Reindent and reformat _plot.py

* update tests

* Move matplotlib drawer into its own file + add test coverage

* Use regular expressions to rewrite and shorten gate names

* Change internal storage format for CircuitDrawerMatplotlib

* Better graphics and adapt plot functions to new internal format

- Support for new internal format
- Resulting quantum circuit figure whould work better with scaling
- Large quantum circuits will now result in wider figure instead of
  squeezing everything into the default matplotlib size
- Some support for multi-target qubit gates
- General code cleanup
- Dropped support for double lines when qubit is in classical state

* Complete test coverage + add some checks for to_draw() inputs

* Compatibility with matplotlib 2.2.3

* Remove compatibility code for MacOSX.

Use local matplotlibrc if necessary instead.

* Add matplotlib dependency to requirements.txt

* Fix non-UTF8 character in file

* Fix .travis.yml

* Remove unnecessary PNG files

* Add CircuitDrawerMatplotlib to documentation and minor code fix

* Fix docstring for CircuitDrawerMatplotlib

Co-authored-by: Nguyen Damien <ngn.damien@gmail.com>

.travis.yml

@@ -42,6 +42,9 @@ install:
   - if [ "${PYTHON:0:1}" = "3" ]; then pip$PY install dormouse; fi
   - pip$PY install -e .
 
+before_script:
+  - "echo 'backend: Agg' > matplotlibrc"
+
 # command to run tests
 script: export OMP_NUM_THREADS=1 && pytest projectq --cov projectq
 

docs/projectq.backends.rst

@@ -5,6 +5,7 @@ backends
 
 	projectq.backends.CommandPrinter
 	projectq.backends.CircuitDrawer
+	projectq.backends.CircuitDrawerMatplotlib
 	projectq.backends.Simulator
 	projectq.backends.ClassicalSimulator
 	projectq.backends.ResourceCounter

projectq/backends/__init__.py

@@ -26,7 +26,7 @@
 * an interface to the IBM Quantum Experience chip (and simulator).
 """
 from ._printer import CommandPrinter
-from ._circuits import CircuitDrawer
+from ._circuits import CircuitDrawer, CircuitDrawerMatplotlib
 from ._sim import Simulator, ClassicalSimulator
 from ._resource import ResourceCounter
 from ._ibm import IBMBackend

projectq/backends/_circuits/__init__.py

@@ -13,4 +13,8 @@
 #   limitations under the License.
 
 from ._to_latex import to_latex
+from ._plot import to_draw
+
 from ._drawer import CircuitDrawer
+from ._drawer_matplotlib import CircuitDrawerMatplotlib
+

projectq/backends/_circuits/_drawer.py

@@ -15,8 +15,6 @@
 Contains a compiler engine which generates TikZ Latex code describing the
 circuit.
 """
-import sys
-
 from builtins import input
 
 from projectq.cengines import LastEngineException, BasicEngine
@@ -223,12 +221,13 @@ def _print_cmd(self, cmd):
             self._free_lines.append(qubit_id)
 
         if self.is_last_engine and cmd.gate == Measure:
-            assert (get_control_count(cmd) == 0)
+            assert get_control_count(cmd) == 0
+
             for qureg in cmd.qubits:
                 for qubit in qureg:
                     if self._accept_input:
                         m = None
-                        while m != '0' and m != '1' and m != 1 and m != 0:
+                        while m not in ('0', '1', 1, 0):
                             prompt = ("Input measurement result (0 or 1) for "
                                       "qubit " + str(qubit) + ": ")
                             m = input(prompt)

projectq/backends/_circuits/_drawer_matplotlib.py

@@ -0,0 +1,208 @@
+#   Copyright 2020 ProjectQ-Framework (www.projectq.ch)
+#
+#   Licensed under the Apache License, Version 2.0 (the "License");
+#   you may not use this file except in compliance with the License.
+#   You may obtain a copy of the License at
+#
+#       http://www.apache.org/licenses/LICENSE-2.0
+#
+#   Unless required by applicable law or agreed to in writing, software
+#   distributed under the License is distributed on an "AS IS" BASIS,
+#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#   See the License for the specific language governing permissions and
+#   limitations under the License.
+"""
+Contains a compiler engine which generates matplotlib figures describing the
+circuit.
+"""
+
+from builtins import input
+import re
+import itertools
+
+from projectq.cengines import LastEngineException, BasicEngine
+from projectq.ops import (FlushGate, Measure, Allocate, Deallocate)
+from projectq.meta import get_control_count
+from projectq.backends._circuits import to_draw
+
+# ==============================================================================
+
+
+def _format_gate_str(cmd):
+    param_str = ''
+    gate_name = str(cmd.gate)
+    if '(' in gate_name:
+        (gate_name, param_str) = re.search(r'(.+)\((.*)\)', gate_name).groups()
+        params = re.findall(r'([^,]+)', param_str)
+        params_str_list = []
+        for param in params:
+            try:
+                params_str_list.append('{0:.2f}'.format(float(param)))
+            except ValueError:
+                if len(param) < 8:
+                    params_str_list.append(param)
+                else:
+                    params_str_list.append(param[:5] + '...')
+
+        gate_name += '(' + ','.join(params_str_list) + ')'
+    return gate_name
+
+
+# ==============================================================================
+
+
+class CircuitDrawerMatplotlib(BasicEngine):
+    """
+    CircuitDrawerMatplotlib is a compiler engine which using Matplotlib library
+    for drawing quantum circuits
+    """
+    def __init__(self, accept_input=False, default_measure=0):
+        """
+        Initialize a circuit drawing engine(mpl)
+        Args:
+            accept_input (bool): If accept_input is true, the printer queries
+                the user to input measurement results if the CircuitDrawerMPL
+                is the last engine. Otherwise, all measurements yield the
+                result default_measure (0 or 1).
+            default_measure (bool): Default value to use as measurement
+                results if accept_input is False and there is no underlying
+                backend to register real measurement results.
+        """
+        BasicEngine.__init__(self)
+        self._accept_input = accept_input
+        self._default_measure = default_measure
+        self._map = dict()
+        self._qubit_lines = {}
+
+    def is_available(self, cmd):
+        """
+        Specialized implementation of is_available: Returns True if the
+        CircuitDrawerMatplotlib is the last engine
+        (since it can print any command).
+
+        Args:
+            cmd (Command): Command for which to check availability (all
+                Commands can be printed).
+
+        Returns:
+            availability (bool): True, unless the next engine cannot handle
+            the Command (if there is a next engine).
+        """
+        try:
+            # Multi-qubit gates may fail at drawing time if the target qubits
+            # are not right next to each other on the output graphic.
+            return BasicEngine.is_available(self, cmd)
+        except LastEngineException:
+            return True
+
+    def _process(self, cmd):
+        """
+        Process the command cmd and stores it in the internal storage
+
+        Queries the user for measurement input if a measurement command
+        arrives if accept_input was set to True. Otherwise, it uses the
+        default_measure parameter to register the measurement outcome.
+
+        Args:
+            cmd (Command): Command to add to the circuit diagram.
+        """
+        if cmd.gate == Allocate:
+            qubit_id = cmd.qubits[0][0].id
+            if qubit_id not in self._map:
+                self._map[qubit_id] = qubit_id
+            self._qubit_lines[qubit_id] = []
+            return
+
+        if cmd.gate == Deallocate:
+            return
+
+        if self.is_last_engine and cmd.gate == Measure:
+            assert get_control_count(cmd) == 0
+            for qureg in cmd.qubits:
+                for qubit in qureg:
+                    if self._accept_input:
+                        measurement = None
+                        while measurement not in ('0', '1', 1, 0):
+                            prompt = ("Input measurement result (0 or 1) for "
+                                      "qubit " + str(qubit) + ": ")
+                            measurement = input(prompt)
+                    else:
+                        measurement = self._default_measure
+                    self.main_engine.set_measurement_result(
+                        qubit, int(measurement))
+
+        targets = [qubit.id for qureg in cmd.qubits for qubit in qureg]
+        controls = [qubit.id for qubit in cmd.control_qubits]
+
+        ref_qubit_id = targets[0]
+        gate_str = _format_gate_str(cmd)
+
+        # First find out what is the maximum index that this command might
+        # have
+        max_depth = max(
+            len(self._qubit_lines[qubit_id])
+            for qubit_id in itertools.chain(targets, controls))
+
+        # If we have a multi-qubit gate, make sure that all the qubit axes
+        # have the same depth. We do that by recalculating the maximum index
+        # over all the known qubit axes.
+        # This is to avoid the possibility of a multi-qubit gate overlapping
+        # with some other gates. This could potentially be improved by only
+        # considering the qubit axes that are between the topmost and
+        # bottommost qubit axes of the current command.
+        if len(targets) + len(controls) > 1:
+            max_depth = max(
+                len(self._qubit_lines[qubit_id])
+                for qubit_id in self._qubit_lines)
+
+        for qubit_id in itertools.chain(targets, controls):
+            depth = len(self._qubit_lines[qubit_id])
+            self._qubit_lines[qubit_id] += [None] * (max_depth - depth)
+
+            if qubit_id == ref_qubit_id:
+                self._qubit_lines[qubit_id].append(
+                    (gate_str, targets, controls))
+            else:
+                self._qubit_lines[qubit_id].append(None)
+
+    def receive(self, command_list):
+        """
+        Receive a list of commands from the previous engine, print the
+        commands, and then send them on to the next engine.
+
+        Args:
+            command_list (list<Command>): List of Commands to print (and
+                potentially send on to the next engine).
+        """
+        for cmd in command_list:
+            if not isinstance(cmd.gate, FlushGate):
+                self._process(cmd)
+
+            if not self.is_last_engine:
+                self.send([cmd])
+
+    def draw(self, qubit_labels=None, drawing_order=None):
+        """
+        Generates and returns the plot of the quantum circuit stored so far
+
+        Args:
+            qubit_labels (dict): label for each wire in the output figure.
+                Keys: qubit IDs, Values: string to print out as label for
+                that particular qubit wire.
+            drawing_order (dict): position of each qubit in the output
+                graphic. Keys: qubit IDs, Values: position of qubit on the
+                qubit line in the graphic.
+
+        Returns:
+            A tuple containing the matplotlib figure and axes objects
+        """
+        max_depth = max(
+            len(self._qubit_lines[qubit_id]) for qubit_id in self._qubit_lines)
+        for qubit_id in self._qubit_lines:
+            depth = len(self._qubit_lines[qubit_id])
+            if depth < max_depth:
+                self._qubit_lines[qubit_id] += [None] * (max_depth - depth)
+
+        return to_draw(self._qubit_lines,
+                       qubit_labels=qubit_labels,
+                       drawing_order=drawing_order)