D.15.5.8 central1st

Usage:

central1st(U1,U2,var); U1, U2 are the names of occuring derivatives, var is a variable in the basering;

Return:

type vector; gives a predefined approximation of the first-order-central-approximation as often used in literature;

Note:

see also forward,laxfrT,setinitials,scheme;

LIB "finitediff.lib";
list D="Ut","Ux","Uy","U";
list V="t","x","y";
list P="a","b";
setinitials(V,D,P);
central1st(Ux,U,x);
==> [0,(2*dx)*x,0,-x^2+1]
central1st(Uy,U,y);
==> [0,0,(2*dy)*y,-y^2+1]