Question on Debugging a code line

[subhabangalore at gmail.com]

On Sunday, May 11, 2014 11:50:32 AM UTC+5:30, subhaba... at gmail.com wrote:
> On Sunday, May 11, 2014 12:57:34 AM UTC+5:30, subhaba... at gmail.com wrote:
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> > Dear Room,
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> > I was trying to go through a code given in http://en.wikipedia.org/wiki/Forward%E2%80%93backward_algorithm[ Forward Backward is an algorithm of Machine Learning-I am not talking on that
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> > I am just trying to figure out a query on its Python coding.]
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> > I came across the following codes.
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> > >>> states = ('Healthy', 'Fever')
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> > 
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> > >>> end_state = 'E'
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> > 
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> > >>> observations = ('normal', 'cold', 'dizzy')
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> > 
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> > >>> start_probability = {'Healthy': 0.6, 'Fever': 0.4}
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> > 
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> > >>> transition_probability = {
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> > 
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> >    'Healthy' : {'Healthy': 0.69, 'Fever': 0.3, 'E': 0.01},
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> >    'Fever' : {'Healthy': 0.4, 'Fever': 0.59, 'E': 0.01},
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> >    }
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> > 
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> > >>> emission_probability = {
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> > 
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> >    'Healthy' : {'normal': 0.5, 'cold': 0.4, 'dizzy': 0.1},
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> >    'Fever' : {'normal': 0.1, 'cold': 0.3, 'dizzy': 0.6},
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> >    }
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> > def fwd_bkw(x, states, a_0, a, e, end_st):
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> >     L = len(x)
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> > 
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> >     fwd = []
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> > 
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> >     f_prev = {} #THE PROBLEM 
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> > 
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> >     # forward part of the algorithm
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> > 
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> >     for i, x_i in enumerate(x):
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> >         f_curr = {}
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> >         for st in states:
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> >             if i == 0:
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> >                 # base case for the forward part
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> >                 prev_f_sum = a_0[st]
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> >             else:
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> >                 prev_f_sum = sum(f_prev[k]*a[k][st] for k in states) ##
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> > 
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> >  
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> >             f_curr[st] = e[st][x_i] * prev_f_sum
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> >  
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> >         fwd.append(f_curr)
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> > 
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> >         f_prev = f_curr
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> >  
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> >     p_fwd = sum(f_curr[k]*a[k][end_st] for k in states)
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> > As this value was being called in prev_f_sum = sum(f_prev[k]*a[k][st] for k in states marked ## 
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> > I wanted to know what values it is generating.
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> > So, I had made the following experiment, after 
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> > for i, x_i in enumerate(x): 
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> > I had put print f_prev 
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> > but I am not getting how f_prev is getting the values.
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> > Here, 
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> > x=observations,
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> > states= states,
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> > a_0=start_probability,
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> > a= transition_probability,
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> > e=emission_probability,
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> > end_st= end_state
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> > Am I missing any minor aspect?
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> > Code is running fine. 
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> > If any one of the esteemed members may kindly guide me.
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> > Regards,
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> > 
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> > Subhabrata Banerjee.
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> 
> Dear Sir,
> 
> Thank you for your kind reply. I will check. 
> 
> Regards,
> 
> Subhabrata Banerjee.

Dear Sir,
Thank you. It worked. I made another similar statement over another set of values on your reply it went nice.
Regards,
Subhabrata Banerjee.