2 Copyright (C) 2008-2014 EDF R&D
4 This file is part of SALOME ADAO module.
6 This library is free software; you can redistribute it and/or
7 modify it under the terms of the GNU Lesser General Public
8 License as published by the Free Software Foundation; either
9 version 2.1 of the License, or (at your option) any later version.
11 This library is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 Lesser General Public License for more details.
16 You should have received a copy of the GNU Lesser General Public
17 License along with this library; if not, write to the Free Software
18 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
20 See http://www.salome-platform.org/ or email : webmaster.salome@opencascade.com
22 Author: Jean-Philippe Argaud, jean-philippe.argaud@edf.fr, EDF R&D
24 .. index:: single: NonLinearLeastSquares
25 .. _section_ref_algorithm_NonLinearLeastSquares:
27 Calculation algorithm "*NonLinearLeastSquares*"
28 -----------------------------------------------
33 This algorithm realizes a state estimation by variational minimization of the
34 classical :math:`J` function of weighted "Least Squares":
36 .. math:: J(\mathbf{x})=(\mathbf{y}^o-\mathbf{H}.\mathbf{x})^T.\mathbf{R}^{-1}.(\mathbf{y}^o-\mathbf{H}.\mathbf{x})
38 It is similar to the :ref:`section_ref_algorithm_3DVAR`, without its background
39 part. The background, required in the interface, is only used as an initial
40 point for the variational minimization.
42 In all cases, it is recommended to prefer the :ref:`section_ref_algorithm_3DVAR`
43 for its stability as for its behaviour during optimization.
45 Optional and required commands
46 ++++++++++++++++++++++++++++++
48 .. index:: single: Background
49 .. index:: single: Observation
50 .. index:: single: ObservationError
51 .. index:: single: ObservationOperator
52 .. index:: single: Minimizer
53 .. index:: single: Bounds
54 .. index:: single: MaximumNumberOfSteps
55 .. index:: single: CostDecrementTolerance
56 .. index:: single: ProjectedGradientTolerance
57 .. index:: single: GradientNormTolerance
58 .. index:: single: StoreInternalVariables
59 .. index:: single: StoreSupplementaryCalculations
61 The general required commands, available in the editing user interface, are the
65 *Required command*. This indicates the background or initial vector used,
66 previously noted as :math:`\mathbf{x}^b`. Its value is defined as a
67 "*Vector*" or a *VectorSerie*" type object.
70 *Required command*. This indicates the observation vector used for data
71 assimilation or optimization, previously noted as :math:`\mathbf{y}^o`. It
72 is defined as a "*Vector*" or a *VectorSerie* type object.
75 *Required command*. This indicates the observation error covariance matrix,
76 previously noted as :math:`\mathbf{R}`. It is defined as a "*Matrix*" type
77 object, a "*ScalarSparseMatrix*" type object, or a "*DiagonalSparseMatrix*"
81 *Required command*. This indicates the observation operator, previously
82 noted :math:`H`, which transforms the input parameters :math:`\mathbf{x}` to
83 results :math:`\mathbf{y}` to be compared to observations
84 :math:`\mathbf{y}^o`. Its value is defined as a "*Function*" type object or
85 a "*Matrix*" type one. In the case of "*Function*" type, different
86 functional forms can be used, as described in the section
87 :ref:`section_ref_operator_requirements`. If there is some control :math:`U`
88 included in the observation, the operator has to be applied to a pair
91 The general optional commands, available in the editing user interface, are
92 indicated in :ref:`section_ref_assimilation_keywords`. In particular, the
93 optional command "*AlgorithmParameters*" allows to choose the specific options,
94 described hereafter, of the algorithm. See
95 :ref:`section_ref_options_AlgorithmParameters` for the good use of this command.
97 The options of the algorithm are the following:
100 This key allows to choose the optimization minimizer. The default choice is
101 "LBFGSB", and the possible ones are "LBFGSB" (nonlinear constrained
102 minimizer, see [Byrd95]_, [Morales11]_ and [Zhu97]_), "TNC" (nonlinear
103 constrained minimizer), "CG" (nonlinear unconstrained minimizer), "BFGS"
104 (nonlinear unconstrained minimizer), "NCG" (Newton CG minimizer). It is
105 strongly recommended to stay with the default.
108 This key allows to define upper and lower bounds for every state variable
109 being optimized. Bounds have to be given by a list of list of pairs of
110 lower/upper bounds for each variable, with possibly ``None`` every time
111 there is no bound. The bounds can always be specified, but they are taken
112 into account only by the constrained optimizers.
115 This key indicates the maximum number of iterations allowed for iterative
116 optimization. The default is 15000, which is very similar to no limit on
117 iterations. It is then recommended to adapt this parameter to the needs on
118 real problems. For some optimizers, the effective stopping step can be
119 slightly different due to algorithm internal control requirements.
121 CostDecrementTolerance
122 This key indicates a limit value, leading to stop successfully the
123 iterative optimization process when the cost function decreases less than
124 this tolerance at the last step. The default is 1.e-7, and it is
125 recommended to adapt it to the needs on real problems.
127 ProjectedGradientTolerance
128 This key indicates a limit value, leading to stop successfully the iterative
129 optimization process when all the components of the projected gradient are
130 under this limit. It is only used for constrained optimizers. The default is
131 -1, that is the internal default of each minimizer (generally 1.e-5), and it
132 is not recommended to change it.
134 GradientNormTolerance
135 This key indicates a limit value, leading to stop successfully the
136 iterative optimization process when the norm of the gradient is under this
137 limit. It is only used for non-constrained optimizers. The default is
138 1.e-5 and it is not recommended to change it.
140 StoreInternalVariables
141 This Boolean key allows to store default internal variables, mainly the
142 current state during iterative optimization process. Be careful, this can be
143 a numerically costly choice in certain calculation cases. The default is
146 StoreSupplementaryCalculations
147 This list indicates the names of the supplementary variables that can be
148 available at the end of the algorithm. It involves potentially costly
149 calculations. The default is a void list, none of these variables being
150 calculated and stored by default. The possible names are in the following
151 list: ["BMA", "OMA", "OMB", "Innovation"].
153 *Tips for this algorithm:*
155 As the *"BackgroundError"* command is required for ALL the calculation
156 algorithms in the interface, you have to provide a value, even if this
157 command is not required for this algorithm, and will not be used. The
158 simplest way is to give "1" as a STRING.
163 References to other sections:
164 - :ref:`section_ref_algorithm_3DVAR`
166 Bibliographical references: