class EngeFunction(AbstractQuadFieldSourceFunction): """ The Enge function with parameters from Berz's paper M.Berz, B. Erdelyn, K.Makino Fringe Field Effects in Small Rings of Large Acceptance Phys. Rev STAB, V3, 124001(2000) """ def __init__(self, length_param, acceptance_diameter_param, cutoff_level = 0.01): self.length = length_param self.acceptance_diameter = acceptance_diameter_param self.a_arr = [0.296471,4.533219,-2.270982,1.068627,-0.036391,0.022261] self.normalization= 1.0 self.n_func_points = 500 #-----find cut-off z value self.cutoff_z = self.acceptance_diameter step = self.acceptance_diameter self.cutoff_level = cutoff_level self.cutoff_z = self._findCutOff(step, cutoff_level) #------------------------------------------------------ self.func = Function() self._normalize() def setEngeCoefficients(self,a_arr): """ Sets new values for Enge function's coeffients. """ self.a_arr = a_arr step = self.length/2 self.cutoff_z = self._findCutOff(step, self.cutoff_level) self._normalize() def setCutOffLevel(self,cutoff_level): """ Sets the cutoff level for quad's field """ step = self.length/2 self.cutoff_level = cutoff_level self.cutoff_z = self._findCutOff(step, cutoff_level) self._normalize() def setCutOffZ(self,cutoff_z): """ Sets the cutoff distance from the center of quad's field""" self.cutoff_z = cutoff_z self._normalize() def setLength(self,length): """ Sets the length of quad's field""" self.length = length step = self.length/2.0 self.cutoff_z = self._findCutOff(step, self.cutoff_level) self._normalize() def setAcceptanceDiameter(self,acceptance_diameter): """ Sets the acceptance diameter of the quad """ self.acceptance_diameter = acceptance_diameter step = self.length/2.0 self.cutoff_z = self._findCutOff(step, self.cutoff_level) self._normalize() def setNumberOfPoints(self,n_func_points): """ Sets the number of points in the field function """ self.n_func_points = n_func_points step = self.length/2.0 self.cutoff_z = self._findCutOff(step, self.cutoff_level) self._normalize() def getCuttOffZ(self): """ Returns the cutoff distance from the center of quad's field""" return self.cutoff_z def getNumberOfPoints(self): """ Returns the number of points in the field function """ return self.n_func_points def _getTrueEngeFunc(self, x): """ Returns the quad's field at the distance x from the center """ # x is the distance from the center of the magnet with the iron length l """ x = (math.fabs(x) - self.length/2.0)/self.acceptance_diameter sum_exp = self.a_arr[0] x0 = x for i in range(1,len(self.a_arr)): sum_exp += self.a_arr[i]*x0 x0 *= x if(abs(sum_exp) > 30.): sum_exp = 30.0*sum_exp/abs(sum_exp) return self.normalization/(1.0+math.exp(sum_exp)) def _findCutOff(self,step, cutoff_level): """ Finds the distance from the center where the field is less than cutoff level """ self.normalization = 1.0 init_val = self._getTrueEngeFunc(0.) z = step val = self._getTrueEngeFunc(z)/init_val if(val <= cutoff_level): return z while(val > cutoff_level): z += step val = self._getTrueEngeFunc(z)/init_val z0 = z - step z1 = z step_z = step/self.n_func_points val0 = self._getTrueEngeFunc(z0)/init_val val1 = self._getTrueEngeFunc(z1)/init_val while(abs(z0-z1) > step_z): z_new = (z0+z1)/2.0 val_new = self._getTrueEngeFunc(z_new)/init_val if(val_new <= cutoff_level): z1 = z_new val1 = val_new else: z0 = z_new val0 = val_new self.cutoff_z = (z0+z1)/2.0 return self.cutoff_z def _normalize(self): """ Normalizes the quad field function to the integral of 1 """ self.normalization = 1.0 step = self.cutoff_z/(self.n_func_points - 1) self.func.clean() sum_int = 0. for ind in range(self.n_func_points): z = step*ind val = self._getTrueEngeFunc(z) self.func.add(z,val) sum_int += val sum_int -= (self._getTrueEngeFunc(0.) + self._getTrueEngeFunc(step*(self.n_func_points - 1)))/2.0 sum_int *= 2.0*step self.normalization = 1.0/sum_int self.func.setConstStep(1) def getFuncValue(self,z): """ Returns the quad's field at the distance z from the center """ if(abs(z) >= self.func.getMaxX()): return 0. return self.normalization*self.func.getY(abs(z)) def getFuncDerivative(self,z): """ Returns the derivative of the getFuncValue(z) """ if(abs(z) >= self.func.getMaxX()): return 0. return math.copysign(self.normalization*self.func.getYP(abs(z)),-z) def getLimitsZ(self): """ Returns the tuple with min and max Z value for this field """ z_max = self.func.getMaxX() return (-z_max,z_max)
n = 100
step = 2 * math.pi / n
for i in range(n):
x = step * i + random.uniform(-eps * step, eps * step)
y = FF(x)
f.add(x, y)
f.dump()
# let's check Const step tolerance setting procedure
f.setStepEps(4 * eps)
print "Const step tolerance =", f.getStepEps()
res = f.setConstStep(1)
print "Function has a const step on x-variable res=", res
print "==========================================="
print " x abs(y-y_fit) abs(dy/dx - dy/dx_fit) "
n = 20
step = 0.8 * (f.getMaxX() - f.getMinX()) / (n - 1)
y_dev_max = 0.
yp_dev_max = 0.
for j in range(n):
x = f.getMinX() + 0.0001 + j * step
y = f.getY(x)
yp = f.getYP(x)
y_th = FF(x)
yp_th = FFP(x)
st = "%6.5f " % x + " %10.5f %10.5f " % (abs(y - y_th), abs(yp - yp_th))
print st
class PMQ_Trace3D_Function(AbstractQuadFieldSourceFunction): """ The PMQ Function is a represenatation of the field of permanent quad from Trace3D documantation (p 77): http://laacg.lanl.gov/laacg/services/traceman.pdf """ def __init__(self, length_param, rad_in, rad_out, cutoff_level = 0.01): self.length = length_param self.rad_in = rad_in self.rad_out = rad_out self.cutoff_level = cutoff_level self.normalization = 1.0 self.n_func_points = 500 z_step = length_param/self.n_func_points z_cutoff = self._findCutOff(z_step,cutoff_level) self.z_min = - z_cutoff self.z_max = + z_cutoff self.func = Function() self._normalize() def _findCutOff(self,step, cutoff_level): """ Finds the distance from the center where the field is less than cutoff level """ init_val = self.getPMQ_FuncValue(0.) z = step val = self.getPMQ_FuncValue(z)/init_val if(val <= cutoff_level): return z while(val > cutoff_level): z += step val = self.getPMQ_FuncValue(z)/init_val z0 = z - step z1 = z n_inner_points = 100 step_z = step/n_inner_points val0 = self.getPMQ_FuncValue(z0)/init_val val1 = self.getPMQ_FuncValue(z1)/init_val while(abs(z0-z1) > step_z): z_new = (z0+z1)/2.0 val_new = self.getPMQ_FuncValue(z_new)/init_val if(val_new <= cutoff_level): z1 = z_new val1 = val_new else: z0 = z_new val0 = val_new cutoff_z = (z0+z1)/2.0 return cutoff_z def _normalize(self): """ Normalizes the quad field function to the integral of 1 """ self.normalization = 1.0 step = self.z_max/(self.n_func_points - 1) sum_int = 0. self.func.clean() for ind in range(self.n_func_points): z = step*ind val = self.getPMQ_FuncValue(z) self.func.add(z,val) sum_int += val sum_int -= (self.getPMQ_FuncValue(0.) + self.getPMQ_FuncValue(step*(self.n_func_points - 1)))/2.0 sum_int *= 2.0*step self.normalization = 1.0/sum_int def getLimitsZ(self): """ Returns (z_min,z_max) tuple as longitudinal limits of the quad field. """ return (self.z_min,self.z_max) def pmq_func(self,z): """ This is PMQ function defined at p. 77 of the Trace3D manual. """ r1 = self.rad_in r2 = self.rad_out v1 = 1.0/math.sqrt(1.0+(z/r1)**2) v2 = 1.0/math.sqrt(1.0+(z/r2)**2) f = 0.5*(1-0.125*z*(1.0/r1+1.0/r2)*v1**2*v2**2*(v1**2+v1*v2+v1**2+4+8/v1/v2)/(v1+v2)) return f def getPMQ_FuncValue(self,z): """ Returns the total PMQ quad field distribution """ f = self.pmq_func(z - self.length/2) - self.pmq_func(z + self.length/2) return f def getFuncValue(self,z): """ Returns the quad's field at the distance z from the center """ if(abs(z) >= self.func.getMaxX()): return 0. return self.normalization*self.func.getY(abs(z)) def getFuncDerivative(self,z): """ Returns the derivative of the getFuncValue(z) """ if(abs(z) >= self.func.getMaxX()): return 0. return math.copysign(self.normalization*self.func.getYP(abs(z)),-z)