Fix some theory in step-44 introduction

The deviator tensor involves the  4th-order symmetric identity tensor, not the "normal" 4th-order identity tensor.

diff --git a/examples/step-44/doc/intro.dox b/examples/step-44/doc/intro.dox
index 30660874aa9e65f1632590c126dde827cbf2710f..edd216beb7fa6b4a38f991bdce83606b6fb8752a 100644 (file)
--- a/examples/step-44/doc/intro.dox
+++ b/examples/step-44/doc/intro.dox
@@ -260,7 +260,7 @@ Similarly, the Kirchhoff stress can be decomposed into volumetric and isochoric
        \boldsymbol{\tau}_{\text{iso}} &=
                2 \mathbf{b} \dfrac{\partial \Psi_{\textrm{iso}} (\overline{\mathbf{b}})}{\partial \mathbf{b}}
                \\
-               &= \underbrace{( \mathcal{I} - \dfrac{1}{3} \mathbf{I} \otimes \mathbf{I})}_{\mathbb{P}} : \overline{\boldsymbol{\tau}} \, ,
+               &= \underbrace{( \mathcal{S} - \dfrac{1}{3} \mathbf{I} \otimes \mathbf{I})}_{\mathbb{P}} : \overline{\boldsymbol{\tau}} \, ,
 @f}
 where
 $p \dealcoloneq \dfrac{\partial \Psi_{\text{vol}}(J)}{\partial J}$ is the pressure response.