rhs_generate.py

# This file is part of QuTiP: Quantum Toolbox in Python.
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import os
import numpy as np
from types import FunctionType, BuiltinFunctionType
from functools import partial

from qutip.cy.codegen import Codegen
from qutip.solver import Options, config
from qutip.qobj import Qobj
from qutip.superoperator import spre, spost


def rhs_clear():
    """
    Resets the string-format time-dependent Hamiltonian parameters.

    Parameters
    ----------

    Returns
    -------
    Nothing, just clears data from internal config module.

    """
    # time-dependent (TD) function stuff
    config.tdfunc = None     # Placeholder for TD RHS function.
    config.colspmv = None    # Placeholder for TD col-spmv function.
    config.colexpect = None  # Placeholder for TD col_expect function.
    config.string = None     # Holds string of variables to be passed to solver
    config.tdname = None     # Name of td .pyx file (used in parallel mc code)


def rhs_generate(H, c_ops, args={}, options=Options(), name=None,
                 cleanup=True):
    """
    Generates the Cython functions needed for solving the dynamics of a
    given system using the mesolve function inside a parfor loop.

    Parameters
    ----------
    H : qobj
        System Hamiltonian.

    c_ops : list
        ``list`` of collapse operators.

    args : dict
        Arguments for time-dependent Hamiltonian and collapse operator terms.

    options : Options
        Instance of ODE solver options.

    name: str
        Name of generated RHS

    cleanup: bool
        Whether the generated cython file should be automatically removed or
        not.

    Notes
    -----
    Using this function with any solver other than the mesolve function
    will result in an error.

    """
    config.reset()
    config.options = options

    if name:
        config.tdname = name
    else:
        config.tdname = "rhs" + str(os.getpid()) + str(config.cgen_num)

    Lconst = 0

    Ldata = []
    Linds = []
    Lptrs = []
    Lcoeff = []

    # loop over all hamiltonian terms, convert to superoperator form and
    # add the data of sparse matrix represenation to

    msg = "Incorrect specification of time-dependence: "

    for h_spec in H:
        if isinstance(h_spec, Qobj):
            h = h_spec

            if not isinstance(h, Qobj):
                raise TypeError(msg + "expected Qobj")

            if h.isoper:
                Lconst += -1j * (spre(h) - spost(h))
            elif h.issuper:
                Lconst += h
            else:
                raise TypeError(msg + "expected operator or superoperator")

        elif isinstance(h_spec, list):
            h = h_spec[0]
            h_coeff = h_spec[1]

            if not isinstance(h, Qobj):
                raise TypeError(msg + "expected Qobj")

            if h.isoper:
                L = -1j * (spre(h) - spost(h))
            elif h.issuper:
                L = h
            else:
                raise TypeError(msg + "expected operator or superoperator")

            Ldata.append(L.data.data)
            Linds.append(L.data.indices)
            Lptrs.append(L.data.indptr)
            Lcoeff.append(h_coeff)

        else:
            raise TypeError(msg + "expected string format")

    # loop over all collapse operators
    for c_spec in c_ops:
        if isinstance(c_spec, Qobj):
            c = c_spec

            if not isinstance(c, Qobj):
                raise TypeError(msg + "expected Qobj")

            if c.isoper:
                cdc = c.dag() * c
                Lconst += spre(c) * spost(c.dag()) - 0.5 * spre(cdc) \
                                                   - 0.5 * spost(cdc)
            elif c.issuper:
                Lconst += c
            else:
                raise TypeError(msg + "expected operator or superoperator")

        elif isinstance(c_spec, list):
            c = c_spec[0]
            c_coeff = c_spec[1]

            if not isinstance(c, Qobj):
                raise TypeError(msg + "expected Qobj")

            if c.isoper:
                cdc = c.dag() * c
                L = spre(c) * spost(c.dag()) - 0.5 * spre(cdc) \
                                             - 0.5 * spost(cdc)
                c_coeff = "(" + c_coeff + ")**2"
            elif c.issuper:
                L = c
            else:
                raise TypeError(msg + "expected operator or superoperator")

            Ldata.append(L.data.data)
            Linds.append(L.data.indices)
            Lptrs.append(L.data.indptr)
            Lcoeff.append(c_coeff)

        else:
            raise TypeError(msg + "expected string format")

    # add the constant part of the lagrangian
    if Lconst != 0:
        Ldata.append(Lconst.data.data)
        Linds.append(Lconst.data.indices)
        Lptrs.append(Lconst.data.indptr)
        Lcoeff.append("1.0")

    # the total number of liouvillian terms (hamiltonian terms + collapse
    # operators)
    n_L_terms = len(Ldata)

    cgen = Codegen(h_terms=n_L_terms, h_tdterms=Lcoeff, args=args,
                   config=config)
    cgen.generate(config.tdname + ".pyx")

    code = compile('from ' + config.tdname +
                   ' import cy_td_ode_rhs', '<string>', 'exec')
    exec(code, globals())

    config.tdfunc = cy_td_ode_rhs

    if cleanup:
        try:
            os.remove(config.tdname + ".pyx")
        except:
            pass


def _td_format_check(H, c_ops, solver='me'):
    """
    Checks on time-dependent format.
    """
    h_const = []
    h_func = []
    h_str = []
    # check H for incorrect format
    if isinstance(H, Qobj):
        pass
    elif isinstance(H, (FunctionType, BuiltinFunctionType, partial)):
        pass  # n_func += 1
    elif isinstance(H, list):
        for k, H_k in enumerate(H):
            if isinstance(H_k, Qobj):
                h_const.append(k)
            elif isinstance(H_k, list):
                if len(H_k) != 2 or not isinstance(H_k[0], Qobj):
                    raise TypeError("Incorrect hamiltonian specification")
                else:
                    if isinstance(H_k[1], (FunctionType,
                                           BuiltinFunctionType, partial)):
                        h_func.append(k)
                    elif isinstance(H_k[1], str):
                        h_str.append(k)
                    elif isinstance(H_k[1], np.ndarray):
                        h_str.append(k)
                    else:
                        raise TypeError("Incorrect hamiltonian specification")
    else:
        raise TypeError("Incorrect hamiltonian specification")

    # the the whole thing again for c_ops
    c_const = []
    c_func = []
    c_str = []
    if isinstance(c_ops, list):
        for k in range(len(c_ops)):
            if isinstance(c_ops[k], Qobj):
                c_const.append(k)
            elif isinstance(c_ops[k], list):
                if len(c_ops[k]) != 2 or not isinstance(c_ops[k][0], Qobj):
                    raise TypeError(
                        "Incorrect collapse operator specification")
                else:
                    if isinstance(c_ops[k][1], (FunctionType,
                                                BuiltinFunctionType, partial)):
                        c_func.append(k)
                    elif isinstance(c_ops[k][1], str):
                        c_str.append(k)
                    elif isinstance(c_ops[k][1], np.ndarray):
                        c_str.append(k)
                    else:
                        raise TypeError(
                            "Incorrect collapse operator specification")
    else:
        raise TypeError("Incorrect collapse operator specification")

    #
    # if n_str == 0 and n_func == 0:
    #     # no time-dependence at all
    #
    if ((len(h_str) > 0 and len(h_func) > 0) or
            (len(c_str) > 0 and len(c_func) > 0)):
        raise TypeError(
            "Cannot mix string and function type time-dependence formats")

    # check to see if Cython is installed and version is high enough.
    if len(h_str) > 0 or len(c_str) > 0:
        try:
            import Cython
        except:
            raise Exception(
                "Unable to load Cython. Use Python function format.")
        else:
            if Cython.__version__ < '0.14':
                raise Exception("Cython version (%s) is too old. Upgrade to " +
                                "version 0.14+" % Cython.__version__)

    if solver == 'me':
        return (len(h_const + c_const),
                len(h_func) + len(c_func),
                len(h_str) + len(c_str))
    elif solver == 'mc':

        #   H      C_ops    #
        #   --     -----    --
        #   NO      NO      00
        #   NO     STR      01
        #   NO     FUNC     02
        #
        #   STR    NO       10
        #   STR    STR      11
        #
        #   FUNC   NO       20
        #
        #   FUNC   FUNC     22

        if isinstance(H, FunctionType):
            time_type = 3
        # Time-indepdent problems
        elif ((len(h_func) == len(h_str) == 0) and
                (len(c_func) == len(c_str) == 0)):
            time_type = 0

        # constant Hamiltonian, time-dependent collapse operators
        elif len(h_func) == len(h_str) == 0:
            if len(c_str) > 0:
                time_type = 1
            elif len(c_func) > 0:
                time_type = 2
            else:
                raise Exception("Error determining time-dependence.")

        # list style Hamiltonian
        elif len(h_str) > 0:
            if len(c_func) == len(c_str) == 0:
                time_type = 10
            elif len(c_str) > 0:
                time_type = 11
            else:
                raise Exception("Error determining time-dependence.")

        # Python function style Hamiltonian
        elif len(h_func) > 0:
            if len(c_func) == len(c_str) == 0:
                time_type = 20
            elif len(c_func) > 0:
                time_type = 22
            else:
                raise Exception("Error determining time-dependence.")

        return time_type, [h_const, h_func, h_str], [c_const, c_func, c_str]


def _td_wrap_array_str(H, c_ops, args, times):
    """
    Wrap numpy-array based time-dependence in the string-based time dependence
    format
    """
    n = 0
    H_new = []
    c_ops_new = []
    args_new = {}

    if not isinstance(H, list):
        H_new = H
    else:
        for Hk in H:
            if isinstance(Hk, list) and isinstance(Hk[1], np.ndarray):
                H_op, H_td = Hk
                td_array_name = "_td_array_%d" % n
                H_td_str = '(0 if (t > %f) else %s[round(%d * (t/%f))])' %\
                    (times[-1], td_array_name, len(times) - 1, times[-1])
                args_new[td_array_name] = H_td
                H_new.append([H_op, H_td_str])
                n += 1
            else:
                H_new.append(Hk)

    if not isinstance(c_ops, list):
        c_ops_new = c_ops
    else:
        for ck in c_ops:
            if isinstance(ck, list) and isinstance(ck[1], np.ndarray):
                c_op, c_td = ck
                td_array_name = "_td_array_%d" % n
                c_td_str = '(0 if (t > %f) else %s[round(%d * (t/%f))])' %\
                    (times[-1], td_array_name, len(times) - 1, times[-1])
                args_new[td_array_name] = c_td
                c_ops_new.append([c_op, c_td_str])
                n += 1
            else:
                c_ops_new.append(ck)

    if args:
        if isinstance(args, dict):
            args_new.update(args)
        elif not args_new:
            args_new = args
        else:
            raise ValueError("Time-dependent array format requires args to " +
                             "be a dictionary")

    return H_new, c_ops_new, args_new