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# Tillsten/exp_sum_pymc.py

Created October 29, 2012 02:56
Fit to an expontial sum in pymc
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 # Make test data t=np.linspace(0,20,200) decays = np.array([2.3,9]) x=np.linspace(-1,1, 32) amp1 = 10*np.exp(-(x+0.5)**2/0.3) amp2 = -8*np.exp(-(x-0.5)**2/0.4) amps=np.column_stack((amp1,amp2)) d=amps.dot(np.exp(-t/decays[:,None])) #Add Noise noise1 = np.linspace(0,0.5,32) np.random.shuffle(noise1) dn=d+noise1[:,None]*np.random.randn(32,t.size) dn+=np.random.randn(1, t.size)*0.4 #Define model sigma=pymc.Uniform('sig',0,1, size=33) amps=pymc.Uniform('amps',-20,20,size=(32,2)) decays=pymc.Uniform('decays',0,20,size=2) base =pymc.exp(-t/decays[:,None]) model= pymc.LinearCombination('fit',[amps],[base]) global_err=pymc.Normal('errs',0,1/sigma[-1]**2, size=t.size) ch_errs=[] for i in range(32): x=pymc.Normal('err'+str(i), model[i,:]+err_e, tau=1/sigma[i]**2, value=dn[i,:],observed=True,size=t.size) ch_errs.append(x) @pymc.potential def orderd(decays=decays): """A pair potential""" return -10000000*(decays[0]-decays[1]>2) # m=pymc.Model([amps, decays, sigma,orderd, model, global_err ]+ch_errs)
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