<s>
In	O
numerical	B-General_Concept
analysis	I-General_Concept
,	O
the	O
mixed	B-Algorithm
finite	I-Algorithm
element	I-Algorithm
method	I-Algorithm
,	O
is	O
a	O
type	O
of	O
finite	B-Application
element	I-Application
method	I-Application
in	O
which	O
extra	O
fields	O
to	O
be	O
solved	O
are	O
introduced	O
during	O
the	O
posing	O
a	O
partial	O
differential	O
equation	O
problem	O
.	O
</s>
<s>
Somewhat	O
related	O
is	O
the	O
hybrid	O
finite	B-Application
element	I-Application
method	I-Application
.	O
</s>
<s>
To	O
be	O
distinguished	O
from	O
the	O
mixed	B-Algorithm
finite	I-Algorithm
element	I-Algorithm
method	I-Algorithm
,	O
usual	O
finite	B-Application
element	I-Application
methods	I-Application
that	O
do	O
not	O
introduce	O
such	O
extra	O
fields	O
are	O
also	O
called	O
irreducible	O
or	O
primal	O
finite	B-Application
element	I-Application
methods	I-Application
.	O
</s>
<s>
The	O
mixed	B-Algorithm
finite	I-Algorithm
element	I-Algorithm
method	I-Algorithm
is	O
efficient	O
for	O
some	O
problems	O
that	O
would	O
be	O
numerically	B-General_Concept
ill-posed	O
if	O
discretized	O
by	O
using	O
the	O
irreducible	O
finite	B-Application
element	I-Application
method	I-Application
;	O
one	O
example	O
of	O
such	O
problems	O
is	O
to	O
compute	O
the	O
stress	B-Algorithm
and	I-Algorithm
strain	I-Algorithm
fields	O
in	O
an	O
almost	O
incompressible	O
elastic	O
body	O
.	O
</s>
<s>
These	O
enforcements	O
are	O
"	O
weak	B-Algorithm
"	O
,	O
i.e.	O
</s>
