Re: help sprandsym

[David Bateman]

Riccardo Corradini wrote:
> Dear all,
> I am using octave2.9.9 CVS when I ru the following program
> n = 500; density = 0.1; knum=0.5;
>
> for i=1:5
>     density = density*0.5;
>     X = sprandsym(n,density);
>     y = randn(n,1);
>     tic; b = X\y; time1 = toc;
>     xf = full(X);
>     tic; b = xf\y; time2 = toc;
>     fprintf('# of non-zero elements in X = %6d \n',nnz(X));
>     fprintf('sparse matrix solution time = %8.3f \n',time1);
>     fprintf('full matrix solution   time = %8.3f \n',time2);
> endfor
>
> I obtain
>
> error: number of rows must match (251 != 250) near line 69, column 47
> error: evaluating assignment expression near line 68, column 9
> error: evaluating if command near line 64, column 5
> error: evaluating if command near line 36, column 3
> error: called from `sprandsym' in file
> `/usr/share/octave/2.9.9+/m/sparse/sprandsym.m'
> error: evaluating assignment expression near line 6, column 4
> error: evaluating for command near line 4, column 1
> error: near line 14 of file `example22.m'
>
> Could you please help me?
> Thanks a lot
> Riccardo
>
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oppps, seems you've found a bug.. sprandsym doesn't currently work for
even values of "n"... The attached patch fixes it..

D.

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David Bateman                                address@hidden
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*** ./scripts/sparse/sprandsym.m.orig25 2006-10-10 18:10:29.000000000 +0200
--- ./scripts/sparse/sprandsym.m        2007-01-23 15:24:33.247271272 +0100
***************
*** 39,45 ****
      S = S + tril(S,-1)';
    elseif nargin == 2
      m1 = floor(n/2);
!     n1 = m1 + 1;
      mn1 = m1*n1;
      k1 = round(d*mn1);
      idx1=unique(fix(rand(min(k1*1.01,k1+10),1)*mn1))+1; 
--- 39,45 ----
      S = S + tril(S,-1)';
    elseif nargin == 2
      m1 = floor(n/2);
!     n1 = m1 + rem(n,2);
      mn1 = m1*n1;
      k1 = round(d*mn1);
      idx1=unique(fix(rand(min(k1*1.01,k1+10),1)*mn1))+1;