For two integers $$k>0$$
k
>
0
and $$\ell $$
ℓ
, a graph $$G=(V,E)$$
G
=
(
V
,
E
)
is called $$(k,\ell )$$
(
k
,
ℓ
)
-tight if $$|E|=k|V|-\ell $$
|
E
|
=
k
|
V
|
-
ℓ
and $$i_G(X)\le k|X|-\ell $$
i
G
(
X
)
≤
k
|
X
|
-
ℓ
for each $$X\subseteq V$$
X
⊆
V
for which $$i_G(X)\ge 1$$
i
G
(
X
)
≥
1
, where $$i_G(X)$$
i
G
(
X
)
denotes the number of induced edges by X. G is called $$(k,\ell )$$
(
k
,
ℓ
)
-redundant if $$G-e$$
G
-
e
has a spanning $$(k,\ell )$$
(
k
,
ℓ
)
-tight subgraph for all $$e\in E$$
e
∈
E
. We consider the following augmentation problem. Given a graph $$G=(V,E)$$
G
=
(
V
,
E
)
that has a $$(k,\ell )$$
(
k
,
ℓ
)
-tight spanning subgraph, find a graph $$H=(V,F)$$
H
=
(
V
,
F
)
with the minimum number of edges, such that $$G\cup H$$
G
∪
H
is $$(k,\ell )$$
(
k
,
ℓ
)
-redundant. We give a polynomial algorithm and a min-max theorem for this augmentation problem when the input is $$(k,\ell )$$
(
k
,
ℓ
)
-tight. For general inputs, we give a polynomial algorithm when $$k\ge \ell $$
k
≥
ℓ
and show the NP-hardness of the problem when $$k<\ell $$
k
<
ℓ
. Since $$(k,\ell )$$
(
k
,
ℓ
)
-tight graphs play an important role in rigidity theory, these algorithms can be used to make several types of rigid frameworks redundantly rigid by adding a smallest set of new bars.