Dirichlet model 'stepSize' could be a vector, also add 'initValue' vector

[ritukeshbharali]

The current Dirichlet model allows a scalar 'stepSize' and vector 'factors', where the in-homogeneous Dirichlet values (factor not equal to zero) for dof type 'i' is modified as: total[i] += factor[i] * stepSize. The input file code snippet looks like this:

falcon/src/constraints/DirichletModel.cpp

Lines 17 to 24 in 778b2dd

	* model =
	* {
	* type = "Dirichlet";
	* nodeGroups = "TopNodes";
	* dofs = "dy";
	* factors = [ -1.];
	* stepSize = 0.001;
	* };

Instead, introduce a more generic Dirichlet expression, total[i] += factor[i] * stepSize[i], where 'i' is a dof type associated with a node group. Also, total[i] would assume values from initVals[i]. In this way, one can model homogeneous conditions with factor and initVal set to zero, in-homogeneous but constant with initVal not equal to zero and factor zero, and in-homogeneous and temporally changing values with non-zero factor.