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The material type for prescribed isotropic active contraction, in a solid mixture of unconstrained materials, is “prescribed isotropic active contraction”. This material must be combined with a stable compressible material that acts as a passive matrix, using a “solid mixture” container as described in Section 4.1.3.22↑. The following material parameters need to be defined:

<material id="1" type="solid mixture">
  <mat_axis type="local">0,0,0</mat_axis>
  <solid type="neo-Hookean">
    <E>1.0</E>
    <v>0</v>
  </solid>
  <solid type="prescribed isotropic active contraction">
    <T0 lc="2">1</T0>
  </solid>
</material>