Re: building a list containing elements f(i,j)
- To: mathgroup at smc.vnet.net
- Subject: [mg71063] Re: building a list containing elements f(i,j)
- From: Jean-Marc Gulliet <jeanmarc.gulliet at gmail.com>
- Date: Wed, 8 Nov 2006 06:01:59 -0500 (EST)
- Organization: The Open University, Milton Keynes, UK
- References: <eimr3e$dhv$1@smc.vnet.net>
xarnaudx at gmail.com wrote:
> hi,
> i want to construct a list of the form:
> { f[1,1], ... f[n,m] }
> So the list contains elements of the form f[i,j] with i ranging from 0
> to n, and j from 0 to somebound[i].
>
> What would be the most elegant way to this?
> thanks
>
You can use either *Table* or *Array*, then *Flatten* the resulting
2D-list to make it one dimensional. Beware that Mathematica use the one
-- and not zero -- to index lists or arrays. You will find hereafter
several example of list construction, some of them with the second index
depending on the value of the first one.
In[1]:=
l1 = Flatten[Table[f[i, j], {i, 0, 3}, {j, 0, 2}]]
Out[1]=
{f[0, 0], f[0, 1], f[0, 2], f[1, 0], f[1, 1], f[1, 2],
f[2, 0], f[2, 1], f[2, 2], f[3, 0], f[3, 1], f[3, 2]}
In[2]:=
l2 = Flatten[Array[f, {4, 3}, {0, 0}]]
Out[2]=
{f[0, 0], f[0, 1], f[0, 2], f[1, 0], f[1, 1], f[1, 2],
f[2, 0], f[2, 1], f[2, 2], f[3, 0], f[3, 1], f[3, 2]}
In[3]:=
l1 == l2
Out[3]=
True
In[4]:=
Table[f[i, j], {i, 0, 3}, {j, 0, i/2}]
Out[4]=
{{f[0, 0]}, {f[1, 0]}, {f[2, 0], f[2, 1]},
{f[3, 0], f[3, 1]}}
In[5]:=
somebound[i_] := {4, 1, 3, 2}[[i + 1]];
Table[f[i, j], {i, 0, 3}, {j, 0, somebound[i]}]
Out[6]=
{{f[0, 0], f[0, 1], f[0, 2], f[0, 3], f[0, 4]},
{f[1, 0], f[1, 1]}, {f[2, 0], f[2, 1], f[2, 2],
f[2, 3]}, {f[3, 0], f[3, 1], f[3, 2]}}
HTH,
Jean-Marc