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D.15.4.21 ParToVar
Procedure from library finitediff.lib (see finitediff_lib).
- Usage:
- ParToVar(f); f a poly in the basering;
- Return:
- type poly; gives back the poly obtained by substituting par(i) by var(i), for the first nvars(basering parameters. Does only make sense, if setinitials is executed before -> nvars <= npars. Is the opposite action to VarToPar, see example ParToVar;
Example:
| | LIB "finitediff.lib";
list D="Ut","Ux","Uy","U";
list V="t","x","y";
list P="a","b";
setinitials(V,D,P);////does not show the ring, as there is no output
basering;///does show the ring
==> // coefficients: QQ(I, T, Px, Py, Cx, Cy, Sx, Sy, a, b, 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
poly f=t**3*cx**2-cy**2*dt+i**3*sx/dt*dx;
f;
==> (dx)/(dt)*i^3*sx+t^3*cx^2+(-dt)*cy^2
def g=VarToPar(f);
g;
==> (I^3*Sx*dx+T^3*Cx^2*dt-Cy^2*dt^2)/(dt)
def h=ParToVar(g);
h==f;
==> 1
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