Python：使用Decimal对np.ndarray进行阶乘

Question

I am trying to make a fraction of factorials in a function. This fraction contains big number so i use Decimal to pass them through, I have two list r and n that I first convert to np.array and I use scipy.misc.factorial for the factorial and try to force calculation with Decimal.

import scipy.misc as scM

def LRT(r,n):
     return Decimal(scM.factorial(np.array(n)))/Decimal(scM.factorial(np.array(r)))

But I get the following error :

    TypeError: Cannot convert array([ inf,  inf,  inf,  inf,  inf]) to Decimal

The error is logical but I don't see how I can perform my calculations with all this constraints

Edit : I use scipy.minimize to do some optimisation on this function. When I try @zondo suggestion :

return np.array(map(Decimal, (scM.factorial(np.array(n)))))/np.array(map(Decimal, (scM.factorial(np.array(r)-1))))

I get the following error :

decimal.InvalidOperation: (+-)INF/(+-)INF

Answer 1

I guess that your values are too big to fit in the numpy.float64 format. let :

n,r=nr=randint(0,1000,(2,10))   

Then :

In [7]: scM.factorial(n)
Out[7]: 
array([              inf,               inf,               inf,
                     inf,   1.40500612e+051,               inf,
         2.48091408e+109,               inf,               inf,
         1.14628056e+170])

If it is the problem, all computations must be done with the Decimal module:

maxi=nr.max()+1
fact=empty(maxi,object)
fact[0]=Decimal(1) 
for i in range(1,maxi) :fact[i]=fact[i-1]*i
res = fact[n]/fact[r]

Then:

In [8]: res
Out[8]: 
array([Decimal('1.336968892230304730842136747E-1929'),
       Decimal('5.449748658873386365158990318E+1043'),
       Decimal('2.310919470411918843300593208E+1276'),
       Decimal('3.935786060399813919328612177E+1163'),
       Decimal('5.459985199929802328950162777E+1655'),
       Decimal('6.284598705467681430195924361E-2217'),
       Decimal('1.144104288612524663561821431E-1280'),
       Decimal('7.165867721516773886182595222E+1136'),
       Decimal('1.844064027516274886503591410E+530'),
       Decimal('1.596549217532394091033873077E-530')], dtype=object)