source: sasview/sansmodels/src/sans/models/DebyeModel.py @ 76b5220

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Last change on this file since 76b5220 was 26e4a24, checked in by Gervaise Alina <gervyh@…>, 15 years ago

reverse previous unittest

  • Property mode set to 100644
File size: 3.0 KB
Line 
1#!/usr/bin/env python
2"""
3    Provide F(x) = 2( exp(-x) + x - 1 )/x**2
4    with x = (q*R_g)**2
5   
6    Debye function as a BaseComponent model
7"""
8
9from sans.models.BaseComponent import BaseComponent
10import math
11
12class DebyeModel(BaseComponent):
13   
14    """
15        Class that evaluates a Debye model.
16       
17        F(x) = 2( exp(-x) + x - 1 )/x**2
18        with x = (q*R_g)**2
19       
20        The model has three parameters:
21            Rg     =  radius of gyration
22            scale  =  scale factor
23            bkd    =  Constant background
24    """
25       
26    def __init__(self):
27        """ Initialization """
28       
29        # Initialize BaseComponent first, then sphere
30        BaseComponent.__init__(self)
31       
32        ## Name of the model
33        self.name = "Debye"
34        self.description="""
35        F(x) = 2( exp(-x) + x - 1 )/x**2
36        with x = (q*R_g)**2
37       
38        The model has three parameters:
39        Rg     =  radius of gyration
40        scale  =  scale factor
41        bkd    =  Constant background
42        """
43        ## Define parameters
44        self.params = {}
45        self.params['rg']          = 50.0
46        self.params['scale']       = 1.0
47        self.params['background']  = 0.0
48
49        ## Parameter details [units, min, max]
50        self.details = {}
51        self.details['rg']         = ['[A]', None, None]
52        self.details['scale']      = ['', None, None]
53        self.details['background'] = ['[1/cm]', None, None]
54        #list of parameter that cannot be fitted
55        self.fixed= []     
56    def _debye(self, x):
57        """
58            Evaluate F(x)= scale * D + bkd
59            has 2 internal parameters :
60                    D = 2 * (exp(-y) + y - 1)/y**2
61                    y = (x * Rg)^(2)
62        """
63        # Note that a zero denominator value will raise
64        # an exception
65        y = (x * self.params['rg'])**2.0
66        if x == 0:
67            D=1
68        else:
69           D = 2.0*( math.exp(-y) + y -1.0 )/y**2.0
70        return self.params['scale']* D + self.params['background']
71   
72    def run(self, x = 0.0):
73        """ Evaluate the model
74            @param x: input q-value (float or [float, float] as [r, theta])
75            @return: (debye value)
76        """
77        if x.__class__.__name__ == 'list':
78            return self._debye(x[0])
79        elif x.__class__.__name__ == 'tuple':
80            raise ValueError, "Tuples are not allowed as input to BaseComponent models"
81        else:
82            return self._debye(x)
83   
84    def runXY(self, x = 0.0):
85        """ Evaluate the model
86            @param x: input q-value (float or [float, float] as [qx, qy])
87            @return: debye value
88        """
89        if x.__class__.__name__ == 'list':
90            q = math.sqrt(x[0]**2 + x[1]**2)
91            return self._debye(q)
92        elif x.__class__.__name__ == 'tuple':
93            raise ValueError, "Tuples are not allowed as input to BaseComponent models"
94        else:
95            return self._debye(x)
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