Changed: Register the primary solution field as "displacement" for the

staggered solver, such that input files with initial condition setup for the
monolithic version also can be used by the staggered solver without issues

SIMDynElasticity.h

@@ -90,7 +90,8 @@ class SIMDynElasticity : public Sim
 
     bool ok = this->setMode(SIM::INIT);
     this->setQuadratureRule(Dim::opt.nGauss[0],true);
-    this->registerField("solution",dSim.getSolution());
+    this->registerField(phOrder > 1 ? "solution" : "displacement",
+                        dSim.getSolution());
     return this->setInitialConditions() && ok;
   }