Fixed minor bugs to increase runtime

changed misc.diag_nd to use a for loop on the domain, which will be collapsed.

Added misc.rat to compute rational approximations of real numbers

Added quantity.EquidistantDomain to simplify the initialization of a domain with a certain step size

Fixed signals/SmoothStep to use spline wise interpolation instead of symbolic computation

+misc/diagNd.m

@@ -29,7 +29,7 @@ function value = diagNd(value, dimensionsToBeDiagonalized)
 	% diagonalization are at the beginning
 	value = permute(value, [dimensionsToBeDiagonalized, ...
 		originalOrder(all(originalOrder ~= dimensionsToBeDiagonalized(:)))]);
-	
+
 	% the result contains the diagonalized dimension first, then the
 	% remaining
 	tempValueSize = size(value);
@@ -60,4 +60,4 @@ function result = allEqual(a)
 		result = (a{1} == a{2});
 	end
 		
-end
\ No newline at end of file
+end

+misc/diag_nd.m

@@ -36,22 +36,10 @@ if valueSize(1) ~= valueSize(2)
 		'be calculated must be quadratic but size(value, 1) ~= size(value, 2)']);
 end
 
-% valueDiagSize is initialised and written in such weired way in the
-% following to ensure that it a vector with at least 2 elements, even if 
-% the variable value is 2D. If this is not done, the final reshape wont
-% work.
-valueDiagSize = ones(1:max((numel(valueSize)-1), 2));
-valueDiagSize(1:numel(valueSize([1, 3:end]))) = valueSize([1, 3:end]); 
-% The implemenetation with num2cell and diag(blkdiag(...)) is terribly slow
-% because of blkdiag. Since it is slower than for-loops and diag, for-loops
-%  are used instead.
-% valueCell = num2cell(value, 1:2); % valueDiagUnshaped = diag(blkdiag(valueCell{:}));
-valueUnshaped = reshape(value, valueSize(1), valueSize(2), []);
-valueDiagUnshaped = zeros(valueSize(1), prod(valueSize(3:end)));
-for it = 1:prod(valueSize(3:end))
-	valueDiagUnshaped(:,it) = diag(valueUnshaped(:, :, it));
+% just do an iteration over the dimensions for the diagonal evaluation.
+valueDiag = zeros([valueSize(2:end), 1]);
+for i = 1:valueSize(1)
+	valueDiag(i,:) = value(i,i,:);
 end
 
-valueDiag = reshape(valueDiagUnshaped, valueDiagSize);
-
 end

+misc/rat.m

+function [approx] = rat(X, tol)
+%RAT_K Rational approximation.
+%   approx = RAT(X,tol) returns a cell with the rational approximations of
+%   real valued X. 
+% X is approximated by
+%
+%                              1
+%         d1 + ----------------------------------
+%                                 1
+%              d2 + -----------------------------
+%                                   1
+%                   d3 + ------------------------
+%                                      1
+%                        d4 + -------------------
+%                                        1
+%                             d5 + --------------
+%                                           1
+%                                  d6 + ---------
+%                                             1
+%                                       d7 + ----
+%                                             d8
+%
+%	in order to chose an approximation of an required tolerance, all
+%	approximation steps will be returned. So APPROX is a cell of the same
+%	dimension as X. Each entry in X is a struct-array with the fields
+%	N for the nominator, D for the denominator, j for the index in X and
+%	error for the absolute error of this approximation. 
+%	For further details, see matlab function rat.
+%	
+%	see rat
+
+if nargin < 2
+    tol = 1.e-6*norm(X(isfinite(X)),1);
+end
+
+assert( all( isreal(X(:)) & isfinite(X(:))));
+
+for j = 1:numel(X)
+	k = 0;
+	C = [1 0; 0 1];
+	x = X(j);
+	while 1
+		k = k+1;
+		d = round(x);
+		
+		x = x - d;
+		C = [C*[d;1] C(:,1)];
+		
+		xError = abs(C(1,1)/C(2,1) - X(j));
+
+		o.N = C(1,1)/sign(C(2,1));
+		o.D = abs(C(2,1));
+		o.j = j;
+		o.error = xError;
+		
+		rationals(k) = o;		
+		
+		if (x==0) || (xError <= max(tol,eps(X(j))))
+			break
+		end
+		x = 1/x;
+	end
+	approx{j} = rationals(:);
+end
+end
+

+numeric/@interpolant/interpolant.m

@@ -91,21 +91,21 @@ classdef interpolant
 		end
 		
 		function value = evaluate(obj, varargin)
-% Example:
-%	test_2p5_1_1 = testInterpolant.evaluate(2.5, 1:5, 1)
-%
-% INPUT PARAMETERS:
-%	NUMERIC.INTERPOLANT		  obj : interpolant object
-%	VARARGIN			 varargin : sample points for which the values are
-%									interpolated. Expected to be a list of
-%									arrays
-% OUTPUT:
-%	ARRAY					value : values at the points specified by varargin				
+			% Example:
+			%	test_2p5_1_1 = testInterpolant.evaluate(2.5, 1:5, 1)
+			%
+			% INPUT PARAMETERS:
+			%		 obj : interpolant object VARARGIN
+			%	varargin : sample points for which the values are
+			%			   interpolated. Expected to be a list of arrays
+			% OUTPUT:
+			%	   value : values at the points specified by varargin
 			% evaluate is used to get the value of the data at certain
 			% points specified by varargin. It is assumed that
 			%	numel(varargin) == ndims(valueOriginal)
 			reducedGrid = varargin(obj.reducedDimension);
-			value = permute(obj.reducedGriddedInterpolant(reducedGrid), obj.permutationVector);
+			interpolant = obj.reducedGriddedInterpolant(reducedGrid);
+			value = permute(interpolant, obj.permutationVector);
 		end
 		
 		function value = eval(obj, varargin)

+quantity/Discrete.m

@@ -234,7 +234,7 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 	end
 	
 	methods (Access = public)
-		function [d, I, d_size] = compositionDomain(obj, domainName)
+		function d = compositionDomain(obj, domainName)
 			
 			assert(isscalar(obj));
 					
@@ -243,17 +243,8 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 			% the evaluation of obj.on( compositionDomain ) is done by:
 			d_size = size(d);
 			
-			% 1) vectorization of the n-d-grid: compositionDomain	
-			d = d(:);
-
-			% 2) then it is sorted in ascending order
-			[d, I] = sort(d);			
-			
-			% verify the domain to be monotonical increasing
-			deltaCOD = diff(d);
-			assert(misc.alln(deltaCOD >= 0), 'The domain for the composition f(g(.)) must be monotonically increasing');
-
-			d = quantity.Domain(domainName, d);
+			% vectorization of the n-d-grid: compositionDomain	
+			d = quantity.Domain(domainName, d(:));
 		end
 		
 		function obj_hat = compose(obj, g, optionalArgs)
@@ -276,11 +267,11 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 				'Composition of functions: The domains for the composition must be equal. A grid join is not implemented yet.');
 			assert( any( logOfDomain )  )
 			
-			% 2) get the composition domain:
+			% get the composition domain:
 			%	For the argument y of a function f(y) which should be
 			%	composed by y = g(z,t) a new dommain will be created on the
 			%	basis of evaluation of g(z,t).
-			[composeOnDomain, I, domainSize] = ...
+			composeOnDomain = ...
 				g.compositionDomain(myCompositionDomain.name);
 			
 			% check if the composition domain is in the range of definition
@@ -290,14 +281,20 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 					'The composition domain is not a subset of obj.domain! The missing values will be extrapolated.');
 			end			
 			
-			% 3) evaluation on the new grid:
+			% evaluation on the new grid:
 			%	the order of the domains is important. At first, the
 			%	domains which will not be replaced are taken. The last
 			%	domain must be the composed domain. For example: a function
 			%	f(x, y, z, t), where y should be composed with g(z, t) will
 			%	be resorted to f_(x, z, t, y) and then evaluated with y =
 			%	g(z,t)
+			
+			% #TODO: optimize the memory consumption of this function.
+			%	1) only consider the unqiue grid points in evaluationDomain
+			%	2) do the conversion of the evaluationDomain directly to
+			%	the target domain.			
 			evaluationDomain = [originalDomain( ~logOfDomain ), composeOnDomain ];
+			
 			newValues = obj.on( evaluationDomain );
 			
 			% reshape the new values into a 2-d array so that the first
@@ -306,20 +303,16 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 			sizeOldDomain = prod( [originalDomain( ~logOfDomain ).n] );
 			sizeComposeDomain = composeOnDomain.gridLength;
 			newValues = reshape(newValues, [sizeOldDomain, sizeComposeDomain]);
-			
-			% 4) reorder the computed values, dependent on the sort
-			% position fo the new domain
-			newValues(:,I) = newValues(:,:);
-			
-			% 5) rearrange the computed values, to have the same dimension
+
+			%rearrange the computed values, to have the same dimension
 			% as the required domain
-			% *) consider the domain 
+			% consider the domain 
 			%		f( z, g(z,t) ) = f(z, g(zeta,t) )|_{zeta = z}
 			tmpDomain = [originalDomain( ~logOfDomain ), g(1).domain ];
 			% newValues will be reshaped into the form
 			%	f(z, t, zeta)
 			newValues = reshape( newValues, [tmpDomain.gridLength, 1] );
-			% *) now the common domains, i.e., zeta = z must be merged:
+			% now the common domains, i.e., zeta = z must be merged:
 			%	for this, find the index of the common domain in list of
 			%	temporary combined domain
 			
@@ -329,10 +322,15 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 			if ~isempty(intersectDomain)
 				
 				idx = 1:length(tmpDomain);
-				idxCommon = idx(strcmp({tmpDomain.name}, intersectDomain));
-
-				% take the diagonal values of the common domain, i.e., z = zeta
-				newValues = misc.diagNd( newValues, idxCommon );
+				logCommon = strcmp({tmpDomain.name}, intersectDomain);
+				
+				% take the diagonal values of the common domain, i.e., z = zeta		
+				% use the diag_nd function because it seems to be faster
+				% then the diagNd function, although the values must be
+				% sorted.
+				% #TODO: Rewrite the diagNd function, using for loops, in order to be as fast as diag_nd
+				newValues = permute( newValues, [idx(logCommon), idx(~logCommon)]);
+				newValues = misc.diag_nd(newValues);
 			end
 			
 			% *) build a new valueDiscrete on the correct grid.		
@@ -366,10 +364,9 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 					value = obj.obj2value(obj(1).domain);
 					
 				elseif nargin == 2 && (iscell(myDomain) || isnumeric(myDomain))
-					% case 1: a domain is specified by myDomain == grid(-cell)
+					% case 1: a domain is specified by myDomain as agrid
 					myDomain = misc.ensureIsCell(myDomain);
 					newGrid = myDomain;
-					myDomain = quantity.Domain.empty();
 
 					if obj(1).isConstant()
 						gridNames = repmat({''}, length(newGrid));
@@ -377,11 +374,14 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 						gridNames = {obj(1).domain.name};
 					end
 
+					% initialize the new domain
+					clear('myDomain');
+					myDomain(1:length(newGrid)) = quantity.Domain();					
 					for k = 1:length(newGrid)
 						myDomain(k) = quantity.Domain(gridNames{k}, newGrid{k});
 					end
 					value = reshape(obj.obj2value(myDomain), ...
-						[myDomain.gridLength, size(obj)]);
+						           [myDomain.gridLength, size(obj)]);
 				else
 					% Since in the remaining cases the order of the domains is not 
 					% neccessarily equal to the order in obj(1).domain, this is 
@@ -903,8 +903,12 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 					gridName2Replace = {gridName2Replace.name};
 					
 				elseif nargin == 3
-					
 					gridName2Replace = misc.ensureIsCell(gridName2Replace);
+					for k = 1:numel( gridName2Replace )
+						if isa(gridName2Replace{k}, 'quantity.Domain')
+							gridName2Replace{k} = gridName2Replace{k}.name;
+						end
+					end						
 					values = misc.ensureIsCell(values);
 				end
 				
@@ -1341,28 +1345,7 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 			for it = 1 : numel(obj)
 				newObj(it).valueDiscrete = obj(it).on(newDomain);
 			end
-		end
-		
-		function [lowerBounds, upperBounds] = getBoundaryValues(obj, varargin)
-			% GETBOUNDARYVALUES returns the boundary values of the grid
-			% [lowerBounds, upperBounds] = getBoundaryValues(obj, gridName)
-			% returns the boundary values of the grid, specified by
-			% gridName
-			%
-			% [lowerBounds, upperBounds] = getBoundaryValues(obj) returns
-			% the boudary values of all grids defined for the object.
-			
-			grids = obj(1).grid(obj(1).domain.gridIndex(varargin{:}));
-			lowerBounds = zeros(1, numel(grids));
-			upperBounds = zeros(1, numel(grids));
-			
-			for k = 1:numel(grids)
-				lowerBounds(k) = grids{k}(1);
-				upperBounds(k) = grids{k}(end);
-			end
-			
-		end
-		
+		end	
 	end
 	
 	%% math
@@ -1681,8 +1664,9 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 			%	xNorm = sqrt(int_0^1 x.' * weight * x dz).
 			% The integral domain is specified by integralGrid.
 			
-			if obj.nargin > 1
-				assert(ischar(integralGridName), 'integralGrid must specify a gridName as a char');
+			if nargin > 1
+				integralGridName = misc.ensureIsCell(integralGridName);
+				assert(ischar([integralGridName{:}]), 'integralGrid must specify a gridName as a char');
 			else
 				integralGridName = obj(1).gridName;
 			end
@@ -1693,8 +1677,10 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 			if obj.nargin == 1 && all(strcmp(obj(1).gridName, integralGridName))
 				xNorm = sqrtm(on(int(obj.' * myParser.Results.weight * obj), integralGridName));
 			else
-				xNorm = sqrtm(int(obj.' * myParser.Results.weight * obj, integralGridName));
-				[xNorm.name] = deal(['||', obj(1).name, '||_{L2}']);
+				xNorm = sqrtm( int(obj.' * myParser.Results.weight * obj, integralGridName) );
+				if isa(xNorm, 'quantity.Discrete')
+					[xNorm.name] = deal(['||', obj(1).name, '||_{L2}']);
+				end
 			end
 		end % l2norm()
 		
@@ -1926,69 +1912,40 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 				return
 			end
 			
-			intGridName = obj(1).gridName;
-			[a, b] = obj.getBoundaryValues;
+			if nargin == 1 || nargin == 3
+				% obj.int() -> integrate over all dimensions of this
+				% quantity.
+				intDomain = obj(1).domain;
+			elseif nargin == 2 
+				% obj.int(z) OR obj.int(z, a, b)
+				% integrate over the domain
+				if isa(varargin{1}, 'quantity.Domain')
+					intDomain = varargin{1};
+				else
+					intDomain = obj(1).domain.find( varargin{1} );
+				end
+			elseif nargin == 4
+				% obj.int(z, <domain>, lowerBound, upperBOund)
+				%
+				I = cumInt( obj, varargin{:});
+				return;
+			end
 			
-			if nargin == 1
-				% see default settings.
-			elseif nargin == 2 || nargin == 4
-				% (obj, z) OR (obj, z, a, b)
-				intGridName = varargin{1};
-			elseif nargin == 3
+			if nargin == 3
 				% (obj, a, b)
 				a = varargin{1};
 				b = varargin{2};
+			elseif nargin == 1 || nargin == 2
+				a = [intDomain.lower];
+				b = [intDomain.upper];
 			end
 			
-			if iscell(intGridName) && numel(intGridName) > 1
-				obj = obj.int(intGridName{1}, a(1), b(1));
-				I = obj.int(intGridName{2:end}, a(2:end), b(2:end));
-				return
-			end
-			[idxGrid, isGrid] = obj(1).domain.gridIndex(intGridName);
-			if nargin == 4
-				I = cumInt( obj, varargin{:});
-				return;
-				%
-				% 				assert(all((varargin{2} == a(idxGrid)) & (varargin{3} == b(idxGrid))), ...
-				% 					'only integration from beginning to end of domain is implemented');
-			end
-			
-			%% do the integration over one dimension
-			I = obj.copy();
-			% get index of the variables that should be considered for
-			% integration
+			I = obj.cumInt(intDomain(1), a(1), b(1));
 			
-			[domainIdx{1:obj(1).nargin}] = deal(':');
-			currentGrid = obj(1).grid{ idxGrid };
-			domainIdx{idxGrid} = find(currentGrid >= a(idxGrid) & currentGrid <= b(idxGrid));
-			
-			myGrid = currentGrid(domainIdx{idxGrid});
-
-			for kObj = 1:numel(obj)
-				J = numeric.trapz_fast_nDim(myGrid, obj(kObj).atIndex(domainIdx{:}), idxGrid);
-				
-				% If the quantity is integrated, so that the first
-				% dimension collapses, this dimension has to be shifted
-				% away, so that the valueDiscrete can be set correctly.
-				if size(J,1) == 1
-					J = shiftdim(J);
-				end
-				
-				% create result:
-				I(kObj).valueDiscrete = J;
-				I(kObj).name = ['int(' obj(kObj).name ')'];
-			end
-			
-			if all(isGrid)
-				newDomain = quantity.Domain();
-			else
-				newDomain = quantity.Domain(obj(kObj).gridName{~isGrid}, ...
-					obj(kObj).grid{~isGrid});
+			if numel(intDomain) > 1
+				I = I.int(intDomain(2:end), a(2:end), b(2:end));
+				return
 			end
-			
-			[I.domain] = deal(newDomain);
-			
 		end
 		
 		function result = cumInt(obj, domain, lowerBound, upperBound)
@@ -2023,7 +1980,7 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 			
 			% int_lowerBound^upperBound f(.) =
 			%	F(upperBound) - F(lowerBound)
-			result = result.subs({domain}, upperBound) ...
+			result = result.subs( {domain}, upperBound) ...
 				- result.subs({domain}, lowerBound);
 			if isa(result, 'quantity.Discrete')
 				result.setName(deal(['int(', obj(1).name, ')']));
@@ -2055,8 +2012,7 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete < handle & matlab.mi
 			end
 			
 			% combine both domains with finest grid
-			joinedDomain = gridJoin(A(1).domain, B(1).domain);
-			
+			joinedDomain = join(A(1).domain, B(1).domain);		
 			
 			[aDiscrete] = A.expandValueDiscrete(joinedDomain);
 			[bDiscrete] = B.expandValueDiscrete(joinedDomain);

+quantity/Domain.m

-classdef Domain < handle & matlab.mixin.CustomDisplay & matlab.mixin.Copyable
+classdef (InferiorClasses = {?quantity.EquidistantDomain}) Domain < handle & matlab.mixin.CustomDisplay & matlab.mixin.Copyable
 	%DOMAIN class to describes a range of values on which a function can be defined.
 	
 	% todo:
@@ -16,10 +16,11 @@ classdef Domain < handle & matlab.mixin.CustomDisplay & matlab.mixin.Copyable
 		% a speaking name for this domain; Should be unique, so that the
 		% domain can be identified by the name.
 		name char;
+		
+		n;		% number of discretization points == gridLength
 	end
 	
 	properties (Dependent)
-		n;		% number of discretization points == gridLength
 		lower;		% lower bound of the domain == grid(1)
 		upper;		% upper bound of the domain == grid(end)
 	end
@@ -35,6 +36,7 @@ classdef Domain < handle & matlab.mixin.CustomDisplay & matlab.mixin.Copyable
 			if nargin >= 1
 				obj.grid = grid(:);
 				obj.name = name;
+				obj.n = length(grid);
 			end
 		end % Domain()
 		
@@ -42,14 +44,6 @@ classdef Domain < handle & matlab.mixin.CustomDisplay & matlab.mixin.Copyable
 			i = ones(size(obj.grid));
 		end
 		
-		function n = get.n(obj)
-			if isempty(obj.grid)
-				n = [];
-			else
-				n = length(obj.grid);
-			end
-		end
-		
 		function lower = get.lower(obj)
 			% minimum value of grid = grid(1), since grid must be ascending
 			lower = obj.grid(1);
@@ -139,7 +133,7 @@ classdef Domain < handle & matlab.mixin.CustomDisplay & matlab.mixin.Copyable
 			
 			[joinedGrid, index] = unique({domain1.name, domain2.name}, 'stable');
 			
-			joinedDomain = quantity.Domain.empty;
+			joinedDomain(1 : numel(joinedGrid)) = quantity.Domain();
 			
 			% #todo@domain: the gird comparison seems to be very
 			% complicated
@@ -164,8 +158,8 @@ classdef Domain < handle & matlab.mixin.CustomDisplay & matlab.mixin.Copyable
 					tempDomain1 = domain1(index1);
 					tempDomain2 = domain2(index2);
 					
-					assert(tempDomain1.lower == tempDomain2.lower, 'Grids must have same domain for gridJoin')
-					assert(tempDomain1.upper == tempDomain2.upper, 'Grids must have same domain for gridJoin')
+					assert( numeric.near( tempDomain1.lower, tempDomain2.lower), 'Grids must have same domain for gridJoin')
+					assert( numeric.near( tempDomain1.upper, tempDomain2.upper), 'Grids must have same domain for gridJoin')
 
 					if tempDomain1.gridLength > tempDomain2.gridLength
 						joinedDomain(i) = tempDomain1;

+quantity/EquidistantDomain.m

@@ -3,21 +3,34 @@ classdef EquidistantDomain < quantity.Domain
 	%definition of a function. The discretization points are equally
 	%distributed over the domain.
 	
-	properties
-		Property1
+	properties (Access = protected)
+		stepSize;
 	end
 	
 	methods
-		function obj = untitled(inputArg1,inputArg2)
-			%UNTITLED Construct an instance of this class
-			%   Detailed explanation goes here
-			obj.Property1 = inputArg1 + inputArg2;
+		function obj = EquidistantDomain(name, lower, upper, optArgs)
+			arguments
+				name,
+				lower,
+				upper,
+				optArgs.N = [];
+				optArgs.stepSize = [];
+			end
+			
+			if ~isempty(optArgs.stepSize)
+				grid = lower : optArgs.stepSize : upper;
+			elseif ~isempty(optArgs.N)
+				grid = linspace(lower, upper, optArgs.N);
+			else
+				error('Either number of discretization points or the step size must be defined!')
+			end
+			
+			obj@quantity.Domain(name, grid);
+			obj.stepSize = optArgs.stepSize;
 		end
 		
-		function outputArg = method1(obj,inputArg)
-			%METHOD1 Summary of this method goes here
-			%   Detailed explanation goes here
-			outputArg = obj.Property1 + inputArg;
+		function d = quantity.Domain(obj)
+			d = arrayfun(@(o) quantity.Domain(o.name, o.grid), obj);
 		end
 	end
 end

+quantity/Function.m

@@ -87,8 +87,8 @@ classdef Function < quantity.Discrete
 				% otherwise the function has to be evaluated on the new
 				% domain
 				value = cell(size(obj));
+				ndGrd = myDomain.ndgrid;
 				for k = 1:numel(obj)
-					ndGrd = myDomain.ndgrid;
 					tmp = obj(k).evaluateFunction( ndGrd{:} );
 					value{k} = tmp(:);
 				end					

+quantity/Symbolic.m

@@ -87,7 +87,6 @@ classdef Symbolic < quantity.Function
 % 				if ~all(strcmp(sort({myDomain.name}), sort(variableName)))
 % 					error('If the gridName(s) are set explicitly, they have to be the same as the variable names!')
 % 				end
-				
 				parentVarargin = [{fun}, varargin(:)', {'domain'}, {myDomain}];
 			end
 			% call parent class
@@ -99,21 +98,27 @@ classdef Symbolic < quantity.Function
 					obj = quantity.Symbolic.empty(size(obj));
 				end
 				
+				mySymbolicVariable = ...
+					quantity.Symbolic.getVariable(valueContinuous);
+				
 				% special properties
 				for k = 1:numel(valueContinuous)
-					obj(k).variable = ...
-						quantity.Symbolic.getVariable(valueContinuous); %#ok<AGROW>
+					obj(k).variable = mySymbolicVariable;  %#ok<AGROW>
 					obj(k).valueSymbolic = symb{k}; %#ok<AGROW>
 					obj(k).symbolicEvaluation = ...
 						variableParser.Results.symbolicEvaluation;  %#ok<AGROW>
 				end
+				
+				assert( ~( ~isempty( mySymbolicVariable ) && isempty( myDomain ) ), ...
+					'quantity:Symbolic:Initialisation', ...
+					'If a quantity.Symbolic is initialized with a symbolic variable, a domain is required.');
 			end
 		end
-				
+
 		function itIs = isConstant(obj)
 			itIs = true;
 			for k = 1:numel(obj)
-				itIs = itIs && isempty(symvar(obj(k).sym));
+				itIs = itIs && isempty( obj(k).variable );
 				if ~itIs 
 					break