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D.15.4.2 u
Procedure from library finitediff.lib (see finitediff_lib).
- Usage:
- u(D[,#]); D a string that occurs in the list of @derivatives, # an optional list of integers.
- Return:
- type vector; gives the vector, that corresponds with gen(n)*m, where m is the monomial defined by #
Example:
| | LIB "finitediff.lib";
list D="Ux","Uy","Ut","U";
list P="a","b";
list V="t","x","y";
setinitials(V,D,P);
u(Ux);
==> [1]
u(Ux,2,3,7);
==> [t^2*x^3*y^7]
u(Uy)+u(Ut)-u(Ux);
==> [-1,1,1]
u(U)*234-dx*dt*dy*3*u(Uy);
==> [0,(-3*dt*dx*dy),0,234]
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