Source code for sas.models.PowerLawModel

""" 
    Provide F(x) = scale* (x)^(-m) + bkd
    Power law function as a BaseComponent model
"""
from sas.models.BaseComponent import BaseComponent
import math

[docs]class PowerLawModel(BaseComponent): """ Class that evaluates a Power_Law model. F(x) = scale* (x)^(-m) + bkd The model has three parameters: m = power scale = scale factor bkd = incoherent background """ def __init__(self): """ Initialization """ # Initialize BaseComponent first, then sphere BaseComponent.__init__(self) ## Name of the model self.name = "Power_Law" ## Define parameters self.params = {} self.params['m'] = 4.0 self.params['scale'] = 1.0 self.params['background'] = 0.0 self.description = """ The Power_Law model. F(x) = scale* (x)^(-m) + bkd The model has three parameters: m = power scale = scale factor bkd = incoherent background""" ## Parameter details [units, min, max] self.details = {} self.details['m'] = ['', 0, None] self.details['scale'] = ['', None, None] self.details['background'] = ['[1/cm]', None, None] #list of parameter that cannot be fitted self.fixed = [] def _PowerLaw(self, x): """ Evaluate F(x) = scale* (x)^(-m) + bkd :param x: q-value """ if self.params['m'] > 0 and x == 0: return 1e+32 elif self.params['m'] == 0 and x == 0: return 1 else: return self.params['scale']*math.pow(x, -1.0*self.params['m'])\ + 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: (PowerLaw value) """ if x.__class__.__name__ == 'list': # Take absolute value of Q, since this model is really meant to # be defined in 1D for a given length of Q #qx = math.fabs(x[0]*math.cos(x[1])) #qy = math.fabs(x[0]*math.sin(x[1])) return self._PowerLaw(math.fabs(x[0])) elif x.__class__.__name__ == 'tuple': raise ValueError, "Tuples are not allowed as input to models" else: return self._PowerLaw(x)
[docs] def runXY(self, x = 0.0): """ Evaluate the model @param x: input q-value (float or [float, float] as [qx, qy]) @return: PowerLaw value """ if x.__class__.__name__ == 'list': q = math.sqrt(x[0]**2 + x[1]**2) return self._PowerLaw(q) elif x.__class__.__name__ == 'tuple': raise ValueError, "Tuples are not allowed as input to models" else: return self._PowerLaw(x)