Timing of a simple table operation

*To*: mathgroup at yoda.physics.unc.edu*Subject*: Timing of a simple table operation*From*: Jeffrey K. MacKie-Mason <jmm at umich.edu>*Date*: Fri, 7 Aug 92 13:19:40 EDT

I created a list of numbers with Table, then calculated the product of 1 plus each element in the list. I want to calculate many such products, so I nested this inside another Table, but found that it took *forever* to calculate. I can illustrate this but having the outer Table create only one product of an inner Table, and then do the same thing without the outer Table. The Table-nested approach tool 5 minutes (NeXT '040-25mHz), the piecemeal approach took about 0.3 seconds! I'm pretty new to Mma, and I understand recursion is a tricky beast, but since I can create this massive delay when the outer Table is only one element long I'm baffled. Suggestions? home/jmm.12> math Mathematica 2.0 for NeXT Copyright 1988-91 Wolfram Research, Inc. -- NeXT graphics initialized -- In[1]:= <<Statistics`ContinuousDistributions` In[2]:= rdist = NormalDistribution[(1.1^(1/240)-1),(0.2/240)] Out[2]= NormalDistribution[0.000397205, 0.000833333] In[3]:= annualReturns=Timing[Table[ (Product[ (1+Table[Random[rdist],{240}][[i]]), {i,1,240} ] - 1), {1} ]] Out[3]= {312.933 Second, {0.109928}} In[4]:= y = Timing[Table[Random[rdist],{240}]][[2]] Out[4]= {-0.000684265, < list of 240 numbers suppressed> } In[5]:= Timing[Product[(1+y[[i]]),{i,1,240}]-1] Out[5]= {0.266667 Second, 0.114892} So, the nested Tables took 5 minutes, the direct (two-step) approach less than 0.3 seconds. What dumb thing am I doing? --- Prof. Jeff MacKie-Mason internet: jmm at umich.edu Dept. of Economics bitnet: usergc76 at umichum Univ. of Michigan phone: 313-764-7438 Ann Arbor, MI 48109-1220 fax: 313-763-9181