<s>
In	O
general	O
,	O
the	O
mass	B-General_Concept
matrix	I-General_Concept
depends	O
on	O
the	O
state	O
,	O
and	O
therefore	O
varies	O
with	O
time	O
.	O
</s>
<s>
The	O
mass	B-General_Concept
matrix	I-General_Concept
is	O
the	O
diagonal	B-Algorithm
block	B-Algorithm
matrix	I-Algorithm
where	O
in	O
each	O
block	O
the	O
diagonal	B-Algorithm
elements	O
are	O
the	O
mass	O
of	O
the	O
corresponding	O
particle	O
:	O
</s>
<s>
where	O
is	O
the	O
identity	B-Algorithm
matrix	I-Algorithm
,	O
or	O
more	O
fully	O
:	O
</s>
<s>
For	O
discrete	O
approximations	O
of	O
continuum	O
mechanics	O
as	O
in	O
the	O
finite	B-Application
element	I-Application
method	I-Application
,	O
there	O
may	O
be	O
more	O
than	O
one	O
way	O
to	O
construct	O
the	O
mass	B-General_Concept
matrix	I-General_Concept
,	O
depending	O
on	O
desired	O
computational	O
accuracy	O
and	O
performance	O
.	O
</s>
<s>
For	O
example	O
,	O
a	O
lumped-mass	O
method	O
,	O
in	O
which	O
the	O
deformation	O
of	O
each	O
element	O
is	O
ignored	O
,	O
creates	O
a	O
diagonal	B-Algorithm
mass	B-General_Concept
matrix	I-General_Concept
and	O
negates	O
the	O
need	O
to	O
integrate	O
mass	O
across	O
the	O
deformed	O
element	O
.	O
</s>
