diff --git a/content/zettels/singular_value_decomposition.md b/content/zettels/singular_value_decomposition.md
index 46f769d..1b7c0cc 100644
--- a/content/zettels/singular_value_decomposition.md
+++ b/content/zettels/singular_value_decomposition.md
@@ -10,6 +10,8 @@ Tags
 
 ## SVD of a MIMO system {#svd-of-a-mimo-system}
 
+This is taken from the book [Multivariable feedback control: analysis and design]({{< relref "skogestad07_multiv_feedb_contr" >}}).
+
 We are interested by the physical interpretation of the SVD when applied to the frequency response of a MIMO system \\(G(s)\\) with \\(m\\) inputs and \\(l\\) outputs.
 
 \begin{equation}
@@ -45,7 +47,7 @@ We define \\(u\_1 = \bar{u}\\), \\(v\_1 = \bar{v}\\), \\(u\_k=\ubar{u}\\) and \\
 
 ## SVD to pseudo inverse rectangular matrices {#svd-to-pseudo-inverse-rectangular-matrices}
 
-This is taken from [Singular Value Decomposition]({{< relref "preumont18_vibrat_contr_activ_struc_fourt_edition" >}}).
+This is taken from the book [Vibration Control of Active Structures - Fourth Edition]({{< relref "preumont18_vibrat_contr_activ_struc_fourt_edition" >}}).
 
 The **Singular Value Decomposition** (SVD) is a generalization of the eigenvalue decomposition of a rectangular matrix:
 \\[ J = U \Sigma V^T = \sum\_{i=1}^r \sigma\_i u\_i v\_i^T \\]