Merge remote-tracking branch 'ibm/main' into lazy-import

.editorconfig

@@ -0,0 +1,51 @@
+# This code is part of Qiskit.
+#
+# (C) Copyright IBM 2017, 2021.
+#
+# This code is licensed under the Apache License, Version 2.0. You may
+# obtain a copy of this license in the LICENSE.txt file in the root directory
+# of this source tree or at http://www.apache.org/licenses/LICENSE-2.0.
+#
+# Any modifications or derivative works of this code must retain this
+# copyright notice, and modified files need to carry a notice indicating
+# that they have been altered from the originals.
+
+# EditorConfig sets project-wide editor defaults: https://EditorConfig.org
+
+# top-most EditorConfig file, stop looking higher in the tree
+root = true
+
+# Default settings can be overidden by editorconfig file in a subdir
+# or by a specific glob later in this file
+[*]
+end_of_line = lf
+insert_final_newline = true
+charset = utf-8
+indent_style = space
+trim_trailing_whitespace = true
+
+# Python
+[*.py]
+indent_size = 4
+
+# Javascript
+[*.{js,json}]
+indent_style = space
+indent_size = 2
+
+## Windows files
+# [*.bat]
+# end_of_line = crlf
+
+# Makefile
+[Makefile]
+indent_style = tab
+
+# Markdown
+[*.md]
+# trailing whitespace is used for <br/> in md (yuck)
+trim_trailing_whitespace = false
+
+# YAML
+[*.{yaml,yml}]
+indent_size = 2

README.md

@@ -7,13 +7,13 @@ Qiskit is made up of elements that work together to enable quantum computing. Th
 
 ## Installation
 
-We encourage installing Qiskit via the pip tool (a python package manager), which installs all Qiskit elements, including Terra.
+We encourage installing Qiskit via the pip tool (a python package manager). The following command installs the core Qiskit components, including Terra.
 
 ```bash
 pip install qiskit
 ```
 
-PIP will handle all dependencies automatically and you will always install the latest (and well-tested) version.
+Pip will handle all dependencies automatically and you will always install the latest (and well-tested) version.
 
 To install from source, follow the instructions in the [documentation](https://qiskit.org/documentation/contributing_to_qiskit.html#install-install-from-source-label).
 

azure-pipelines.yml

@@ -33,7 +33,7 @@ stages:
         - bash: |
             set -e
             python -m pip install --upgrade pip
-            pip install cibuildwheel==2.2.2
+            pip install cibuildwheel==2.3.1
             pip install -U twine
             cibuildwheel --output-dir wheelhouse .
         - task: PublishBuildArtifacts@1
@@ -74,7 +74,7 @@ stages:
       - bash: |
           set -e
           python -m pip install --upgrade pip
-          pip install cibuildwheel==2.2.2
+          pip install cibuildwheel==2.3.1
           pip install -U twine
           cibuildwheel --output-dir wheelhouse .
       - task: PublishBuildArtifacts@1
@@ -96,7 +96,7 @@ stages:
       - bash: |
           set -e
           python -m pip install --upgrade pip
-          pip install cibuildwheel==2.2.2
+          pip install cibuildwheel==2.3.1
           pip install -U twine
           cibuildwheel --output-dir wheelhouse .
       - task: PublishBuildArtifacts@1
@@ -107,7 +107,7 @@ stages:
         env:
           TWINE_PASSWORD: $(TWINE_PASSWORD)
     - job: 'Windows'
-      pool: {vmImage: 'vs2017-win2016'}
+      pool: {vmImage: 'windows-latest'}
       condition: startsWith(variables['Build.SourceBranch'], 'refs/tags')
       variables:
         TWINE_USERNAME: qiskit
@@ -123,7 +123,7 @@ stages:
         - bash: |
             set -e
             python -m pip install --upgrade pip
-            pip install cibuildwheel==2.2.2
+            pip install cibuildwheel==2.3.1
             pip install -U twine
             cibuildwheel --output-dir wheelhouse
         - task: PublishBuildArtifacts@1
@@ -182,7 +182,8 @@ stages:
             cp -r test /tmp/terra-tests/.
             cp .stestr.conf /tmp/terra-tests/.
             cp -r .stestr /tmp/terra-tests/. || :
-            sudo apt install -y graphviz
+            sudo apt-get update
+            sudo apt-get install -y graphviz
             pip check
           displayName: 'Install dependencies'
         - bash: |
@@ -239,7 +240,8 @@ stages:
             image_tests/bin/pip install -U -r requirements.txt -c constraints.txt
             image_tests/bin/pip install -U -c constraints.txt -e ".[visualization]"
             image_tests/bin/python setup.py build_ext --inplace
-            sudo apt install -y graphviz pandoc
+            sudo apt-get update
+            sudo apt-get install -y graphviz pandoc
             image_tests/bin/pip check
           displayName: 'Install dependencies'
         - bash: image_tests/bin/python -m unittest discover -v test/ipynb
@@ -313,7 +315,8 @@ stages:
             python -m pip install --upgrade pip setuptools wheel
             pip install -U tox
             python setup.py build_ext --inplace
-            sudo apt install -y graphviz
+            sudo apt-get update
+            sudo apt-get install -y graphviz
           displayName: 'Install dependencies'
         - bash: |
             tox -edocs
@@ -617,7 +620,8 @@ stages:
             pip install -U -c constraints.txt -e .
             pip install -U "qiskit-aer" "z3-solver" -c constraints.txt
             python setup.py build_ext --inplace
-            sudo apt install -y graphviz
+            sudo apt-get update
+            sudo apt-get install -y graphviz
             pip check
           displayName: 'Install dependencies'
         - bash: |
@@ -768,7 +772,8 @@ stages:
             pip install -c constraints.txt -e .
             pip install "qiskit-ibmq-provider" "qiskit-aer" "z3-solver" "qiskit-ignis" "matplotlib>=3.3.0" sphinx nbsphinx sphinx_rtd_theme cvxpy -c constraints.txt
             python setup.py build_ext --inplace
-            sudo apt install -y graphviz pandoc
+            sudo apt-get update
+            sudo apt-get install -y graphviz pandoc
             pip check
           displayName: 'Install dependencies'
         - bash: |

pyproject.toml

@@ -6,8 +6,13 @@ line-length = 100
 target-version = ['py36', 'py37', 'py38', 'py39']
 
 [tool.cibuildwheel]
-manylinux-x86_64-image = "manylinux2010"
-manylinux-i686-image = "manylinux2010"
+manylinux-x86_64-image = "manylinux2014"
+manylinux-i686-image = "manylinux2014"
 skip = "pp* cp36-* *musllinux*"
 test-skip = "cp310-win32 cp310-manylinux_i686"
 test-command = "python {project}/examples/python/stochastic_swap.py"
+# We need to use pre-built versions of Numpy and Scipy in the tests; they have a
+# tendency to crash if they're installed from source by `pip install`, and since
+# Numpy 1.22 there are no i686 wheels, so we force pip to use older ones without
+# restricting any dependencies that Numpy and Scipy might have.
+before-test = "pip install --only-binary=numpy,scipy numpy scipy"

qiskit/algorithms/__init__.py

@@ -114,10 +114,7 @@
    :toctree: ../stubs/
    :nosignatures:
 
-   HHL
-   NumPyLinearSolver
-   LinearSolver
-   LinearSolverResult
+   linear_solvers
 
 
 Minimum Eigensolvers

qiskit/algorithms/linear_solvers/__init__.py

@@ -10,10 +10,83 @@
 # copyright notice, and modified files need to carry a notice indicating
 # that they have been altered from the originals.
 
-"""Linear solvers."""
+"""
+Linear solvers (:mod:`qiskit.algorithms.linear_solvers`)
+=========================================================
+It  contains classical and quantum algorithms to solve systems of linear equations such as
+:class:`~qiskit.algorithms.HHL`.
+Although the quantum algorithm accepts a general Hermitian matrix as input, Qiskit's default
+Hamiltonian evolution is exponential in such cases and therefore the quantum linear solver will
+not achieve an exponential speedup.
+Furthermore, the quantum algorithm can find a solution exponentially faster in the size of the
+system than their classical counterparts (i.e. logarithmic complexity instead of polynomial),
+meaning that reading the full solution vector would kill such speedup (since this would take
+linear time in the size of the system).
+Therefore, to achieve an exponential speedup we can only compute functions from the solution
+vector (the so called observables) to learn information about the solution.
+Known efficient implementations of Hamiltonian evolutions or observables are contained in the
+following subfolders:
+
+`Matrices`_
+  A placeholder for efficient implementations of the Hamiltonian evolution of particular types of
+  matrices.
+
+`Observables`_
+  A placeholder for efficient implementations of functions that can be computed from the solution
+  vector to a system of linear equations.
+
+.. currentmodule:: qiskit.algorithms.linear_solvers
+
+Linear Solvers
+==============
+
+.. autosummary::
+   :toctree: ../stubs/
+   :nosignatures:
+
+   LinearSolver
+   LinearSolverResult
+   HHL
+   NumPyLinearSolver
+
+Matrices
+========
+
+.. autosummary::
+   :toctree: ../stubs/
+   :nosignatures:
+
+   LinearSystemMatrix
+   NumPyMatrix
+   TridiagonalToeplitz
+
+Observables
+===========
+
+.. autosummary::
+    :toctree: ../stubs/
+
+    LinearSystemObservable
+    AbsoluteAverage
+    MatrixFunctional
+
+"""
 
 from .hhl import HHL
 from .numpy_linear_solver import NumPyLinearSolver
 from .linear_solver import LinearSolver, LinearSolverResult
+from .matrices import LinearSystemMatrix, NumPyMatrix, TridiagonalToeplitz
+from .observables import LinearSystemObservable, AbsoluteAverage, MatrixFunctional
 
-__all__ = ["HHL", "NumPyLinearSolver", "LinearSolver", "LinearSolverResult"]
+__all__ = [
+    "HHL",
+    "NumPyLinearSolver",
+    "LinearSolver",
+    "LinearSolverResult",
+    "LinearSystemMatrix",
+    "NumPyMatrix",
+    "TridiagonalToeplitz",
+    "LinearSystemObservable",
+    "AbsoluteAverage",
+    "MatrixFunctional",
+]

qiskit/algorithms/linear_solvers/observables/absolute_average.py

@@ -34,8 +34,9 @@ class AbsoluteAverage(LinearSystemObservable):
 
             import numpy as np
             from qiskit import QuantumCircuit
-            from qiskit.algorithms.linear_solvers.observables.absolute_average import
-             AbsoluteAverage
+            from qiskit.algorithms.linear_solvers.observables.absolute_average import \
+            AbsoluteAverage
+            from qiskit.opflow import StateFn
 
             observable = AbsoluteAverage()
             vector = [1.0, -2.1, 3.2, -4.3]

qiskit/algorithms/linear_solvers/observables/matrix_functional.py

@@ -32,9 +32,10 @@ class MatrixFunctional(LinearSystemObservable):
 
             import numpy as np
             from qiskit import QuantumCircuit
-            from qiskit.algorithms.linear_solvers.observables.matrix_functional import
-             MatrixFunctional
+            from qiskit.algorithms.linear_solvers.observables.matrix_functional import \
+            MatrixFunctional
             from qiskit.transpiler.passes import RemoveResetInZeroState
+            from qiskit.opflow import StateFn
 
             tpass = RemoveResetInZeroState()
 

qiskit/circuit/library/__init__.py

@@ -235,18 +235,6 @@
    PauliEvolutionGate
 
 
-Probability distributions
-=========================
-
-.. autosummary::
-   :toctree: ../stubs/
-   :template: autosummary/class_no_inherited_members.rst
-
-   UniformDistribution
-   NormalDistribution
-   LogNormalDistribution
-
-
 N-local circuits
 ================
 
@@ -426,11 +414,6 @@
     QAOAAnsatz,
 )
 from .data_preparation import PauliFeatureMap, ZFeatureMap, ZZFeatureMap
-from .probability_distributions import (
-    LogNormalDistribution,
-    NormalDistribution,
-    UniformDistribution,
-)
 from .quantum_volume import QuantumVolume
 from .fourier_checking import FourierChecking
 from .graph_state import GraphState

qiskit/circuit/library/basis_change/qft.py

@@ -13,6 +13,7 @@
 """Quantum Fourier Transform Circuit."""
 
 from typing import Optional
+import warnings
 import numpy as np
 
 from qiskit.circuit import QuantumCircuit, QuantumRegister
@@ -229,14 +230,30 @@ def inverse(self) -> "QFT":
         inverted._inverse = not self._inverse
         return inverted
 
+    def _warn_if_precision_loss(self):
+        """Issue a warning if constructing the circuit will lose precision.
+
+        If we need an angle smaller than ``pi * 2**-1022``, we start to lose precision by going into
+        the subnormal numbers.  We won't lose _all_ precision until an exponent of about 1075, but
+        beyond 1022 we're using fractional bits to represent leading zeros."""
+        max_num_entanglements = self.num_qubits - self.approximation_degree - 1
+        if max_num_entanglements > -np.finfo(float).minexp:  # > 1022 for doubles.
+            warnings.warn(
+                "precision loss in QFT."
+                f" The rotation needed to represent {max_num_entanglements} entanglements"
+                " is smaller than the smallest normal floating-point number.",
+                category=RuntimeWarning,
+                stacklevel=3,
+            )
+
     def _check_configuration(self, raise_on_failure: bool = True) -> bool:
         """Check if the current configuration is valid."""
         valid = True
         if self.num_qubits is None:
             valid = False
             if raise_on_failure:
                 raise AttributeError("The number of qubits has not been set.")
-
+        self._warn_if_precision_loss()
         return valid
 
     def _build(self) -> None:
@@ -256,7 +273,9 @@ def _build(self) -> None:
             circuit.h(j)
             num_entanglements = max(0, j - max(0, self.approximation_degree - (num_qubits - j - 1)))
             for k in reversed(range(j - num_entanglements, j)):
-                lam = np.pi / (2 ** (j - k))
+                # Use negative exponents so that the angle safely underflows to zero, rather than
+                # using a temporary variable that overflows to infinity in the worst case.
+                lam = np.pi * (2.0 ** (k - j))
                 circuit.cp(lam, j, k)
 
             if self.insert_barriers: