Re: Re: FactorInteger Print Formatting

*To*: mathgroup at christensen.cybernetics.net*Subject*: [mg767] Re: [mg694] Re: [mg650] FactorInteger Print Formatting*From*: tiggj at iswaps.lonnds.ml.com (Jason Tigg SWAP GROUP ANALYST X2312 LDN)*Date*: Tue, 18 Apr 1995 00:58:05 -0400

Hi, this may be what you want In[1] := Format[ factorform[a_List] ] := StringTake[ Apply[ StringJoin, Map[gform, a]], {1,-2}]; gform[{b_,1}] := ToString[b] <> "*"; gform[{b_,n_}] := ToString[b] <> "^" <> ToString[n] <> "*"; In[2] := 2^12 5^5 199 Out[2] = 2547200000 In[3] := factorform[ FactorInteger[%]] Out[3] = 2^12*5^5*199 jason > > Dear Alan: > > Here is a clue. It is not exactly what you asked for, and it still needs > an automatic way to generate the [[4]] at the end, but I think it is some > progress. > > In[23]:= Trace[FactorInteger[400] /. {a_,b_}->a^b][[4]] > > 5 2 > Out[23]= {2 , 4 } > > If you try to go beyond this kind of list output to the product form you > asked for, the automatic exponent evaluation machinery takes over and > destroys all progress. This is closely related to a question I asked > recently, which I suspect has no answer; viz: How do you prevent > > In[34]:= Sqrt[8] > > Out[34]= 2 Sqrt[2] > > I think what we need is an new option, like AnswerForm->pattern, which > would stop evaluation if the desired pattern is created anywhere along the > evaluation chain. > > Has anybody given any thought to this, WRI? > > Regards- Martin > > >Could anyone suggest a neat way to reformat the output of > >FactorInteger into a more usable print format? > > > >FactorInteger[n] gives a list of prime factors of the integer n > >in ascending order, together with their exponents viz: > > > > FactorInteger[900] produces the list {{2,2},{3,2},{5,2}} > > > >What I need is a function called say factorform[list] such that: > > > > Print[ factorform[{{2,2},{3,2},{5,2}}] ] produces 2^2*3^2*5^2 > > > >Ideally exponents equal to 1 would be suppressed so that when > > > > ff = FactorInteger[30] produces {{2,1},{3,1},{5,1}} then > > > > Print[factorform[ff]] would give 2*3*5 instead of 2^1*3^1*5^1 and > > > > Print[factorform[FactorInteger[2^6*3*5^2*7]]] would give 2^6*3*5^2*7 > > > >A procedural solution is possible, but I was unable to create a simple > >function which would give the desired result. > > > > > >Alan Powell POWELLA at delphi.com > > >