Re: [Help-gsl] Gsl-1.8 compiled and running under MSYS-1.10+second order derivative

[Brian Gough]

Rene Girard wrote:
> gcc  -O2 -Wall -ansi -I/usr/local/include -c -o t_dn2.o t_dn2.c
> t_dn2.c: In function ‘g_x’:
> t_dn2.c:61: warning: dereferencing ‘void *’ pointer
> t_dn2.c:61: error: void value not ignored as it ought to be
>
> double g_x(double x, void *params)
>  {
>   const double pi = 4.0*atan(1.0);    
>   double yo,y1;
>
>   yo = (sin(pi*x/2.0)*sin(pi*params[1]/2));
>   y1 = yo*yo;

With the prototype for g_x() above params[1] is an invalid expression, 
because params has void* type.  Use something like  double *p = params; 
then access elements as p[0], p[1] etc.

--
best regards,

Brian Gough

Network Theory Ltd,
Publishing "An Introduction to GCC"
http://www.network-theory.co.uk/gcc/