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Add optional x1 to provide the scipy secant method with a second guess #3515

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Add optional x1 to provide the scipy secant method with a second guess #3515

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17 changes: 13 additions & 4 deletions openmc/search.py
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Original file line number Diff line number Diff line change
Expand Up @@ -67,8 +67,8 @@ def _search_keff(guess, target, model_builder, model_args, print_iterations,
return keff.n - target


def search_for_keff(model_builder, initial_guess=None, target=1.0,
bracket=None, model_args=None, tol=None,
def search_for_keff(model_builder, initial_guess=None, second_guess=None,
target=1.0, bracket=None, model_args=None, tol=None,
bracketed_method='bisect', print_iterations=False,
run_args=None, **kwargs):
"""Function to perform a keff search by modifying a model parametrized by a
Expand All @@ -82,6 +82,12 @@ def search_for_keff(model_builder, initial_guess=None, target=1.0,
initial_guess : Real, optional
Initial guess for the parameter to be searched in
`model_builder`. One of `guess` or `bracket` must be provided.
second_guess: Real, optional
Second guess for the parameter to be searched in
`model_builder`. If a second guess is not provided, scipy
generates a guess nearby. This option exists to allow the
user to define their own x1 guess, which may improve search
behavior over the scipy default.
target : Real, optional
keff value to search for, defaults to 1.0.
bracket : None or Iterable of Real, optional
Expand Down Expand Up @@ -126,6 +132,8 @@ def search_for_keff(model_builder, initial_guess=None, target=1.0,

if initial_guess is not None:
cv.check_type('initial_guess', initial_guess, Real)
if second_guess is not None:
cv.check_type('second_guess', second_guess, Real)
if bracket is not None:
cv.check_iterable_type('bracket', bracket, Real)
cv.check_length('bracket', bracket, 2)
Expand Down Expand Up @@ -178,9 +186,10 @@ def search_for_keff(model_builder, initial_guess=None, target=1.0,
root_finder = sopt.bisect

elif initial_guess is not None:

# x1 can be None if the user does not provide a second_guess
# in which case, scipy generates a guess near x0
# Generate our arguments
args = {'func': search_function, 'x0': initial_guess}
args = {'func': search_function, 'x0': initial_guess, 'x1': second_guess}
if tol is not None:
args['tol'] = tol

Expand Down