Re: Error in pari/gp code

["Ruud H.G. van Tol" <rvtol@isolution.nl>]

On 2024-03-21 17:10, Swati, NoFirstName wrote:
> I am trying to write a code to output the position of the last 
> non-zero entry of this matrix but the code is giving a syntax error. I 
> am not sure what went wrong. Could someone help in this regard?
>
> Thanks,
> Swati
>
> C = [[1, 2, 3, 4], [7, 9, 10], [25, 31, 0], [0, 0, 0]];
> A = matconcat([C[1]; C[2]; C[3]; C[4]]);
>
> R = 0;
> C = 0;
> S= 0;
>
> for(i = matsize(A)[1], i >= 1 &&  S == 0, i--,
>     for(j = matsize(A)[2], j >= 1 &&  S== 0, j--,
>         if(A[i, j] != 0,
>             R = i;
>             C = j;
>            S = 1;
>             break;
>   )))
>
> if(S == 1,
>     print("Position of the last non-zero entry:" [R, C]),
>     print("Matrix A contains only zeros.")
> );

I didn't get why C[1] has 4 elements, so I made it:

? doit(D=0) = {
  my( a = [ [1,2,3], [7,9,10], [25,31,0], [0,0,0] ], r=0, c=0 );
  a = Mat(a~);
  D && printp(a);
  D && print(matsize(a));

  for( i=1, matsize(a)[1]
  , for( j=1, matsize(a)[2]
    , if( a[i,j], [r,c] = [i,j] )
    )
  );

  if( r
  , print("Position of the last non-zero entry:",[r,c])
  , print("Matrix contains only zeros.")
  );
}

? doit(1)

[ 1  2  3]

[ 7  9 10]

[25 31  0]

[ 0  0  0]

[4, 3]
Position of the last non-zero entry:[3, 2]

-- Ruud