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D.15.10.13 setinitials

Procedure from library finitediff.lib (see finitediff_lib).

Usage:
setinitials(V,D[,P]); V,D,P are lists with strings as elements

Return:
no return value: sets the dependence order of the occuring derivatives, constructs the suitable ring to compute in containing user chosen parameters, sets new basering

Note:
P is optional, used to introduce some additional parameters into the ring. The Sine and Cosine values needed for the fourier transformation are symbolically introduced under the names string(c)+nameof(variable), i.e. if x is any spatial variable then cx:=cosine(dx*ksi), when regarding the fourier transform after ksi (for sine respectively). Artificial parameters I,T,Px,Py are introduced for the later eigenvalue analysis. Variables can be transformed into parameters of similar name

Example:
 
LIB "finitediff.lib";
list D="Ut","Ux","Uy","U";
list V="t","x","y";
list P="alpha","beta","gamma";
setinitials(V,D,P);////does not show the ring, since there is no output
basering;///does show the ring
==> //   characteristic : 0
==> //   14 parameter    : I T Px Py Cx Cy Sx Sy alpha beta gamma dt dx dy 
==> //   minpoly        : 0
==> //   number of vars : 8
==> //        block   1 : ordering c
==> //        block   2 : ordering lp
==> //                  : names    i t x y cx cy sx sy
==> // quotient ring from ideal
==> _[1]=cy^2+sy^2-1
==> _[2]=cx^2+sx^2-1
==> _[3]=i^2+1