Source code for sas.models.DebyeModel

""" 
    Provide F(x) = 2( exp(-x) + x - 1 )/x**2
    with x = (q*R_g)**2
    
    Debye function as a BaseComponent model
"""
from sas.models.BaseComponent import BaseComponent
import math

[docs]class DebyeModel(BaseComponent): """ Class that evaluates a Debye model. F(x) = 2( exp(-x) + x - 1 )/x**2 with x = (q*R_g)**2 The model has three parameters: Rg = radius of gyration scale = scale factor bkd = Constant background """ def __init__(self): """ Initialization """ # Initialize BaseComponent first, then sphere BaseComponent.__init__(self) ## Name of the model self.name = "Debye" self.description = """ F(x) = 2( exp(-x) + x - 1 )/x**2 with x = (q*R_g)**2 The model has three parameters: Rg = radius of gyration scale = scale factor bkd = Constant background """ ## Define parameters self.params = {} self.params['rg'] = 50.0 self.params['scale'] = 1.0 self.params['background'] = 0.0 ## Parameter details [units, min, max] self.details = {} self.details['rg'] = ['[A]', None, None] self.details['scale'] = ['', None, None] self.details['background'] = ['[1/cm]', None, None] #list of parameter that cannot be fitted self.fixed = [] def _debye(self, x): """ Evaluate F(x)= scale * D + bkd has 2 internal parameters : D = 2 * (exp(-y) + y - 1)/y**2 y = (x * Rg)^(2) """ # Note that a zero denominator value will raise # an exception y = (x * self.params['rg'])**2.0 if x == 0: D = 1 else: D = 2.0*( math.exp(-y) + y -1.0 )/y**2.0 return self.params['scale'] * D + self.params['background']
[docs] def run(self, x = 0.0): """ Evaluate the model @param x: input q-value (float or [float, float] as [r, theta]) @return: (debye value) """ if x.__class__.__name__ == 'list': return self._debye(x[0]) elif x.__class__.__name__ == 'tuple': raise ValueError, "Tuples are not allowed as input to models" else: return self._debye(x)
[docs] def runXY(self, x = 0.0): """ Evaluate the model @param x: input q-value (float or [float, float] as [qx, qy]) @return: debye value """ if x.__class__.__name__ == 'list': q = math.sqrt(x[0]**2 + x[1]**2) return self._debye(q) elif x.__class__.__name__ == 'tuple': raise ValueError, "Tuples are not allowed as input to models" else: return self._debye(x)