source: sasview/sansmodels/src/sans/models/PowerLawModel.py @ 768656e

ESS_GUIESS_GUI_DocsESS_GUI_batch_fittingESS_GUI_bumps_abstractionESS_GUI_iss1116ESS_GUI_iss879ESS_GUI_iss959ESS_GUI_openclESS_GUI_orderingESS_GUI_sync_sascalccostrafo411magnetic_scattrelease-4.1.1release-4.1.2release-4.2.2release_4.0.1ticket-1009ticket-1094-headlessticket-1242-2d-resolutionticket-1243ticket-1249ticket885unittest-saveload
Last change on this file since 768656e was 753552d, checked in by Gervaise Alina <gervyh@…>, 16 years ago

description added

  • Property mode set to 100644
File size: 3.0 KB
Line 
1#!/usr/bin/env python
2"""
3    Provide F(x) = scale* (x)^(-m) + bkd
4    Power law function as a BaseComponent model
5"""
6
7from sans.models.BaseComponent import BaseComponent
8import math
9
10class PowerLawModel(BaseComponent):
11   
12    """
13        Class that evaluates a Power_Law model.
14       
15        F(x) = scale* (x)^(-m) + bkd
16       
17        The model has three parameters:
18            m     =  power
19            scale  =  scale factor
20            bkd    =  incoherent background
21    """
22       
23    def __init__(self):
24        """ Initialization """
25       
26        # Initialize BaseComponent first, then sphere
27        BaseComponent.__init__(self)
28       
29        ## Name of the model
30        self.name = "Power_Law"
31
32        ## Define parameters
33        self.params = {}
34        self.params['m']            = 4.0
35        self.params['scale']        = 1.0
36        self.params['background']   = 0.0
37        self.description=""" The Power_Law model.
38        F(x) = scale* (x)^(-m) + bkd
39        The model has three parameters:
40        m     =  power
41        scale  =  scale factor
42        bkd    =  incoherent background"""
43        ## Parameter details [units, min, max]
44        self.details = {}
45        self.details['m']           = ['', 0,    None]
46        self.details['scale']       = ['', None, None]
47        self.details['background']  = ['', None, None]
48               
49    def _PowerLaw(self, x):
50        """
51            Evaluate  F(x) = scale* (x)^(-m) + bkd
52           
53        """
54        if x<0 and self.params['m']>0:
55            raise ValueError, "negative number cannot be raised to a fractional power"
56       
57        return self.params['scale']*math.pow(x ,-1.0*self.params['m'])\
58                + self.params['background']
59       
60    def run(self, x = 0.0):
61        """ Evaluate the model
62            @param x: input q-value (float or [float, float] as [r, theta])
63            @return: (PowerLaw value)
64        """
65        if x.__class__.__name__ == 'list':
66            # Take absolute value of Q, since this model is really meant to
67            # be defined in 1D for a given length of Q
68            #qx = math.fabs(x[0]*math.cos(x[1]))
69            #qy = math.fabs(x[0]*math.sin(x[1]))
70            return self._PowerLaw(math.fabs(x[0]))
71        elif x.__class__.__name__ == 'tuple':
72            raise ValueError, "Tuples are not allowed as input to BaseComponent models"
73        else:
74            return self._PowerLaw(x)
75   
76    def runXY(self, x = 0.0):
77        """ Evaluate the model
78            @param x: input q-value (float or [float, float] as [qx, qy])
79            @return: PowerLaw value
80        """
81        if x.__class__.__name__ == 'list':
82            q = math.sqrt(x[0]**2 + x[1]**2)
83            return self._PowerLaw(q)
84        elif x.__class__.__name__ == 'tuple':
85            raise ValueError, "Tuples are not allowed as input to BaseComponent models"
86        else:
87            return self._PowerLaw(x)
Note: See TracBrowser for help on using the repository browser.