[Help-gsl] root finding

[ghadir mohammadkhani]

Hello,
I want to solve as such integral:
  \Int_{-PI/2}^{PI/2}  \sum_{i} cos(t) (dF(x_i,t)/dy) dt, in which x_i  is 
obtained by solving the equation p(x)=0 , i.e.,  roots of function p are the 
same x_i and the variable x varies between 0 to 1.
To obtain roots, I use subroutine gsl_root_fdfsolver_steffenson,   but receive 
the massage the below:
gsl: steffenson.c:110: ERROR:  function value is not finite.
I think this error is removed with varying the initial guess, but I don't know 
how should substitute it by other initial guess inside several loops. 

Thanks for your guidance,

Ghadir