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Jacobian matrix and the Null pointer
- From: "Haisam K. Ido" <haisam at ido dot org>
- To: gsl-discuss at sources dot redhat dot com
- Date: Tue, 05 Aug 2003 22:02:31 -0400
- Subject: Jacobian matrix and the Null pointer
What is the null pointer in the text below?
ref: http://sources.redhat.com/gsl/ref/gsl-ref_25.html#SEC379
"... int (* jacobian) (double t, const double y[], double * dfdy, double dfdt[],
void * params);
This function should store the vector elements df_i(t,y,params)/dt in the array
dfdt and the Jacobian matrix J_{ij} in the array dfdy regarded as a row-ordered
matrix J(i,j) = dfdy[i * dim + j] where dim is the dimension of the system. Some of
the simpler solver algorithms do not make use of the Jacobian matrix, so it is not
always strictly necessary to provide it (this element of the struct can be replace
by a *null pointer*). However, it is useful to provide the Jacobian to allow the
solver ...."