Bill Allombert on Wed, 18 Jan 2006 18:23:16 +0100 |
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Re: Two suggestions: |
On Wed, Jan 18, 2006 at 03:36:14PM +0000, Prof. J. E. Cremona wrote: > (1) As Bill has reported, although ellsearch() allows one to take from > the database all elliptic curves with a given conductor, it is > inefficient to do this in a loop, say from N=N1 to N=N2, since each call > to ellsearch() causes the entire relevant database file to be read in. > > I suggest adding a function of the form > > forell(E,N1,N2, seq ) which would execute seq for all elliptic curves E > in the database with N1 <= cond(E) <= N2; which would only read each > file once. I will have a look at it. > That's my first wish-list suggestion (of 2006). > > (2) The elliptic curve databes holds each curve's id as a string, for > example "20160cy2". It would be convenient to be able to simply split > this into 3 components, for example [20160,"cy",2]. With Bill's help I > have written a gp function to do this: > > { > code2seq(code)=local(v,N=0,num=0,i=1,i1,class); > v=Vecsmall(code); > while(v[i]<58,N=10*N+v[i]-48;i++); > i1=i; > while(v[i]>57,i++); > class=Strchr(vector(i-i1,j,v[i1+j-1])); > while(i<=length(v),num=10*num+v[i]-48;i++); > [N,class,num] > } > > But this direct manipulation of the vector of ASCII codes is rather > awkward. Surely there would be other places in which some string > manipulation would be helpful? Can we add this to the wish-list please? Well there are about 3 ways to solve that: 1) change ellsearch (etc.) to return curve names in the form [N,class,num] instead of "Nclassnum". 2) Add a GP function ellparsename that convert "Nclassnum" to [N,class,num] 3) Add a more generic string manipulation functions that allow to do the same as code2seq but much simpler. It depends on how much usage each formats has. Cheers, Bill.