# Source code for sasmodels.kernel

"""
Execution kernel interface
==========================

:class:KernelModel defines the interface to all kernel models.
In particular, each model should provide a :meth:KernelModel.make_kernel
call which returns an executable kernel, :class:Kernel, that operates
on the given set of *q_vector* inputs.  On completion of the computation,
the kernel should be released, which also releases the inputs.
"""

from __future__ import division, print_function

# pylint: disable=unused-import
try:
from typing import List, Any
except ImportError:
pass
else:
import numpy as np
from .details import CallDetails
from .modelinfo import ModelInfo
# pylint: enable=unused-import

[docs]class KernelModel(object):
"""
Model definition for the compute engine.
"""
info = None  # type: ModelInfo
dtype = None # type: np.dtype
[docs]    def make_kernel(self, q_vectors):
# type: (List[np.ndarray]) -> "Kernel"
"""
Instantiate a kernel for evaluating the model at *q_vectors*.
"""
raise NotImplementedError("need to implement make_kernel")

[docs]    def release(self):
# type: () -> None
"""
Free resources associated with the kernel.
"""
#print("null release model")
pass

[docs]class Kernel(object):
"""
Instantiated model for the compute engine, applied to a particular *q*.

Subclasses should define *__init__()* to set up the kernel inputs, and
*_call_kernel()* to evaluate the kernel::

def __init__(self, ...):
...
self.q_input = <q-value class with nq attribute>
self.info = <ModelInfo object>
self.dim = <'1d' or '2d'>
self.dtype = <kernel.dtype>
size = 2*self.q_input.nq+4 if self.info.have_Fq else self.q_input.nq+4
size = size + <extra padding if needed for kernel>
self.result = np.empty(size, dtype=self.dtype)

def _call_kernel(self, call_details, values, cutoff, magnetic,
# type: (CallDetails, np.ndarray, np.ndarray, float, bool, int) -> None
... # call <kernel>
nq = self.q_input.nq
if self.info.have_Fq:  # models that compute both F and F^2
end = 2*nq if have_Fq else nq
self.result[0:end:2] = F**2
self.result[1:end:2] = F
else:
end = nq
self.result[0:end] = Fsq
self.result[end + 0] = total_weight
self.result[end + 1] = form_volume
self.result[end + 2] = shell_volume
"""
#: Kernel dimension, either "1d" or "2d".
dim = None  # type: str
#: Model info.
info = None  # type: ModelInfo
#: Numerical precision for the computation.
dtype = None  # type: np.dtype
#: Q values at which the kernel is to be evaluated.
q_input = None  # type: Any
#: Place to hold result of *_call_kernel()* for subclass.
result = None # type: np.ndarray

[docs]    def Iq(self, call_details, values, cutoff, magnetic):
# type: (CallDetails, np.ndarray, np.ndarray, float, bool) -> np.ndarray
r"""
Returns I(q) from the polydisperse average scattering.

.. math::

I(q) = \text{scale} \cdot P(q) + \text{background}

With the correct choice of model and contrast, setting *scale* to
the volume fraction $V_f$ of particles should match the measured
absolute scattering.  Some models (e.g., vesicle) have volume fraction
built into the model, and do not need an additional scale.
"""
_, F2, _, shell_volume, _ = self.Fq(call_details, values, cutoff,
combined_scale = values[0]/shell_volume
background = values[1]
return combined_scale*F2 + background
__call__ = Iq

[docs]    def Fq(self, call_details, values, cutoff, magnetic,
# type: (CallDetails, np.ndarray, np.ndarray, float, bool, int) -> np.ndarray
r"""
Returns <F(q)>, <F(q)^2>, effective radius, shell volume and
form:shell volume ratio.  The <F(q)> term may be None if the
form factor does not support direct computation of $F(q)$

$P(q) = <F^2(q)>/<V>$ is used for structure factor calculations,

.. math::

I(q) = \text{scale} \cdot P(q) \cdot S(q) + \text{background}

For the beta approximation, this becomes

.. math::

I(q) = \text{scale} P (1 + <F>^2/<F^2> (S - 1)) + \text{background}
= \text{scale}/<V> (<F^2> + <F>^2 (S - 1)) + \text{background}

$<F(q)>$ and $<F^2(q)>$ are averaged by polydispersity in shape
and orientation, with each configuration $x_k$ having form factor
$F(q, x_k)$, weight $w_k$ and volume $V_k$.  The result is:

.. math::

P(q)=\frac{\sum w_k F^2(q, x_k) / \sum w_k}{\sum w_k V_k / \sum w_k}

The form factor itself is scaled by volume and contrast to compute the
total scattering.  This is then squared, and the volume weighted
F^2 is then normalized by volume F.  For a given density, the number
of scattering centers is assumed to scale linearly with volume.  Later
scaling the resulting $P(q)$ by the volume fraction of particles
gives the total scattering on an absolute scale. Most models
incorporate the volume fraction into the overall scale parameter.  An
exception is vesicle, which includes the volume fraction parameter in
the model itself, scaling $F$ by $\surd V_f$ so that the math for
the beta approximation works out.

By scaling $P(q)$ by total weight $\sum w_k$, there is no need to make
sure that the polydisperisity distributions normalize to one.  In
particular, any distibution values $x_k$ outside the valid domain
of $F$ will not be included, and the distribution will be implicitly
truncated.  This is controlled by the parameter limits defined in the
model (which truncate the distribution before calling the kernel) as
well as any region excluded using the *INVALID* macro defined within
the model itself.

The volume used in the polydispersity calculation is the form volume
for solid objects or the shell volume for hollow objects.  Shell
volume should be used within $F$ so that the normalizing scale
represents the volume fraction of the shell rather than the entire
form.  This corresponds to the volume fraction of shell-forming

The calculation of $S$ requires the effective radius and the
volume fraction of the particles.  The model can have several
different ways to compute effective radius, with the
*radius_effective_mode* parameter used to select amongst them.  The
volume fraction of particles should be determined from the total
volume fraction of the form, not just the shell volume fraction.
This makes a difference for hollow shapes, which need to scale
the volume fraction by the returned volume ratio when computing $S$.
For solid objects, the shell volume is set to the form volume so
this scale factor evaluates to one and so can be used for both
hollow and solid shapes.
"""
self._call_kernel(call_details, values, cutoff, magnetic,
#print("returned",self.q_input.q, self.result)
nout = 2 if self.info.have_Fq and self.dim == '1d' else 1
total_weight = self.result[nout*self.q_input.nq + 0]
# Note: total_weight = sum(weight > cutoff), with cutoff >= 0, so it
# is okay to test directly against zero.  If weight is zero then I(q),
# etc. must also be zero.
if total_weight == 0.:
total_weight = 1.
# Note: shell_volume == form_volume for solid objects
form_volume = self.result[nout*self.q_input.nq + 1]/total_weight
shell_volume = self.result[nout*self.q_input.nq + 2]/total_weight
if shell_volume == 0.:
shell_volume = 1.
F1 = (self.result[1:nout*self.q_input.nq:nout]/total_weight
if nout == 2 else None)
F2 = self.result[0:nout*self.q_input.nq:nout]/total_weight
return F1, F2, radius_effective, shell_volume, form_volume/shell_volume

[docs]    def release(self):
# type: () -> None
"""
Free resources associated with the kernel instance.
"""
#print("null release kernel")
pass

def _call_kernel(self, call_details, values, cutoff, magnetic,