Initializing the Nonlinear Least-Squares Solver - GNU Scientific Library -- Reference Manual
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### 38.2 Initializing the Solver

— Function: gsl_multifit_fsolver * gsl_multifit_fsolver_alloc (const gsl_multifit_fsolver_type * T, size_t n, size_t p)

> This function returns a pointer to a newly allocated instance of a solver of type T for n observations and p parameters. The number of observations n must be greater than or equal to parameters p.

> If there is insufficient memory to create the solver then the function returns a null pointer and the error handler is invoked with an error code of `GSL_ENOMEM`.

— Function: gsl_multifit_fdfsolver * gsl_multifit_fdfsolver_alloc (const gsl_multifit_fdfsolver_type * T, size_t n, size_t p)

> This function returns a pointer to a newly allocated instance of a derivative solver of type T for n observations and p parameters. For example, the following code creates an instance of a Levenberg-Marquardt solver for 100 data points and 3 parameters,

>               const gsl_multifit_fdfsolver_type * T
>                   = gsl_multifit_fdfsolver_lmder;
>               gsl_multifit_fdfsolver * s
>                   = gsl_multifit_fdfsolver_alloc (T, 100, 3);

> The number of observations n must be greater than or equal to parameters p.

> If there is insufficient memory to create the solver then the function returns a null pointer and the error handler is invoked with an error code of `GSL_ENOMEM`.

— Function: int gsl_multifit_fsolver_set (gsl_multifit_fsolver * s, gsl_multifit_function * f, const gsl_vector * x)

> This function initializes, or reinitializes, an existing solver s to use the function f and the initial guess x.

— Function: int gsl_multifit_fdfsolver_set (gsl_multifit_fdfsolver * s, gsl_multifit_function_fdf * fdf, const gsl_vector * x)

> This function initializes, or reinitializes, an existing solver s to use the function and derivative fdf and the initial guess x.

— Function: void gsl_multifit_fsolver_free (gsl_multifit_fsolver * s)
— Function: void gsl_multifit_fdfsolver_free (gsl_multifit_fdfsolver * s)

> These functions free all the memory associated with the solver s.

— Function: const char * gsl_multifit_fsolver_name (const gsl_multifit_fsolver * s)
— Function: const char * gsl_multifit_fdfsolver_name (const gsl_multifit_fdfsolver * s)

> These functions return a pointer to the name of the solver. For example,

>               printf ("s is a '%s' solver\n",
>                       gsl_multifit_fdfsolver_name (s));

> would print something like `s is a 'lmder' solver`.

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