Karim Belabas on Sun, 30 Mar 2014 09:48:41 +0200

 Re: Unidentified subject!

```* Giacomo Mulas [2014-03-30 09:06]:
> On Fri, 28 Mar 2014, Bill Allombert wrote:
>
> >But your code is doing
> > gmael2(coeffs2,2,4) = stoi(2);
> >so it is modifying the older columns.
> >
> >maybe you wanted to do
> > gmael2(coeffs2,4,2) = stoi(2);
> >in which case you would be correct.
>
> oops, I had assumed that the first index would be the row and the second the
> column, so I thought that gmael2(coeffs2,2,4) meant "second row, fourth
> column". I am now learning from you that it's the reverse, if I understand
> what you mean. This would explain things, indeed.

mael means "Multi-dimensional Array ELement": gmael(x,2,4)
fetches/assigns data corresponding to x[2][4]; more generally,
gmael<n>(x,i1,i2,...,in) is associated to x[i1][i2]...[in].

To consider x as a matrix and fetch x[i,j] as you expected, use gcoeff(x,i,j).

To avoid difficulties, you can use the following to build an mxn matrix,
one column at a time:

GEN m = cgetg(n+1,t_MAT);
for (j = 1; j <= n; j++
{
GEN c;
gel(m, j) = c = cgetg(m+1,t_COL);
for (i = 1; i <= m; i++) gel(c,i) = ...;
}

Cheers,

K.B.
--
Karim Belabas, IMB (UMR 5251)  Tel: (+33) (0)5 40 00 26 17
Universite Bordeaux 1          Fax: (+33) (0)5 40 00 69 50
351, cours de la Liberation    http://www.math.u-bordeaux1.fr/~kbelabas/
F-33405 Talence (France)       http://pari.math.u-bordeaux1.fr/  [PARI/GP]
`

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