[Help-gsl] gsl_sf_legendre_Plm_e sign error

[Robin Hankin]

Hi everyone.

(newbie here.  I've been lurking for a while).


I'm working with Legendre functions and I'm trying to reproduce 
Abramowitz and Stegun's
figure 8.2 which shows $P^1_n(x)$.

Here's the relevant bit of my code.  I am a C novice!   (any advice on coding
style gratefully received).


void legendre_Plm_e(int *l, int *m, double *x, int *nx, double *val, 
double *err, int *status)
{
  int i;
  gsl_sf_result result;
  gsl_set_error_handler_off();

  for(i = 0; i< *nx ; i++){
    status[i]  = gsl_sf_legendre_Plm_e(*l, *m, x[i] , &result) ;
    val[i] = result.val;
    err[i] = result.err;
  }
}


I get a sign error:  A&S have $P_1^1(0) ==1$, and I get -1.


Could anyone confirm that I've not introduced an invisible minus sign 
into my coding?

best wishes



--
Robin Hankin
Uncertainty Analyst
Southampton Oceanography Centre
SO14 3ZH
tel +44(0)23-8059-7743
address@hidden (edit in obvious way; spam precaution)