Computes element coordinate from global coordinate

globalToLocal.m

% local coordinates from global coordinates
function eta = globalToLocal(obj, xPt, nodalX)
	% tolerance
	tol = 1e-13;
	% get an initial guess at [0,0]
	eta = zeros(size(xPt));
	% NR iteration
	deta = 1;
	iter = 0;
	maxIter = 20;
	while norm(deta) > tol
		iter = iter+1;
		if iter > maxIter
			disp('Convergence not met!');
			break;
		end
		N = obj.shapeFun(eta);
		dN_deta = obj.shapeFunDeriv(eta);
		deta = -(nodalX*dN_deta)\(nodalX*N - xPt);
		eta = eta + deta;
	end
end