COMSOL Multiphysics™

flform
Purpose
flform
Convert between PDE forms.
Syntax
Description
fem1 = flform(fem,'outform',form,...)
[equ,bnd] = flform(fem,'outform',form,...)
fem1 = flform(fem,'outform',form,...) converts the FEM structure fem to
a FEM structure fem1 on form. The fields in fem1.equ and fem1.bnd contain the
corresponding fields from fem.equ and fem.bnd converted to the form form.
fem1.form is set to form. All other fields in fem are copied to fem1.
[equ,bnd] = flform(fem,'outform',form,...)
is an alternative syntax, returning only the equ and bnd fields of the FEM structure.
Conversion from coefficient to general form is performed according to
∂u k
Γ lj
= – c lkji
– α
∂ xi lkj
u k
+ γ lj
∂u k
F l
= f l
– β lki
– a
∂ xi lk
u k
G l
= g l
– q lk
u k
R m
= r m
– h ml
u l
using a notation where there is an implicit summation over the k (or l) and i indices
in each product. Affected fields are therefore ga, c, al, f, be and a from equ and g,
q, r and h from bnd, with c, al, be, a, g and q removed and ga, f, r and g
remaining. Other fields within equ and bnd, such as shape, weak, init, var, etc.,
remain unchanged.
Conversion from general form to weak form is performed according to
( n)
W l
( nt)
W l
=
=
( n – 1)
W l
( n)
R m
=
( n)
W l
( nt)
W l
=
R m
∂v l
+ Γ lj
+ F
∂ xj l
v l
∂u kvl
d u kvl
+ d a
+ e
lk∂t
a lk 2
d t
( n – 1)
W l
+ G l
v l
2
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