Re: Suggestions for translating a Do[] loop ...

*To*: mathgroup at smc.vnet.net*Subject*: [mg69800] Re: [mg69773] Suggestions for translating a Do[] loop ...*From*: "Adriano Pascoletti" <pascolet at dimi.uniud.it>*Date*: Sat, 23 Sep 2006 04:45:03 -0400 (EDT)

David, consider two lists In[1]:= n = 10; A = Array[Subscript[a, #1] & , {n - 1}]; B = Array[Subscript[b, #1] & , {n - 1}]; the list r is computed by In[3]:= r = Reverse[FoldList[#2[[1]]*((#2[[2]] + #1)/ (1 + #2[[2]] + #1)) & , 0, Transpose[{Reverse[A], Reverse[B]}]]]; In order to verify the result let In[4]:= f = Function[i, A[[i]]*((B[[i]] + r[[i + 1]])/ (1 + B[[i]] + r[[i + 1]]))]; and compute In[5]:= Function[i, f[i] - r[[i]]] /@ Range[n - 1] Out[5]= {0,0,0,0,0,0,0,0,0} Hope it helps Adriano Pascoletti David Annetts wrote .. > Hi, > > Given that a, b & r are lists of the same length, can anyone suggest a > translation of the following Do[] loop to something functional? It looks > like an ideal application for Fold, but for me, the loop going backwards > is > really obscuring things. > > The loop is > > Do[ > r[[j]] = a[[j]] * (b[[j]] + r[[j + 1]]) / (1 + b[[j]] * r[[j > + 1]]), > {j, Length@a - 1, 1, -1} > ]; > > with r[[Length@a]] = 0. > > Many thanks, > > Dave. >