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D.15.15.13 setinitials

Procedure from library finitediff.lib (see finitediff_lib).

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

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

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

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
==> // coefficients: QQ(I, T, Px, Py, Cx, Cy, Sx, Sy, alpha, beta, gamma, dt,\
    dx, dy)
==> // 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