Fixed subs to work with quantity.EquidistantDomain

+quantity/Discrete.m

@@ -483,6 +483,8 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete ...
 						% compute the permutation index, in order to bring the
 						% new domain in the same order as the original one.
 						gridPermuteIdx = obj(1).domain.getPermutationIdx(myDomain);
+						
+						assert( any(gridPermuteIdx ~= 0), "grid could not be found.")
 					end			
 					% get the valueDiscrete data for this object. Apply the
 					% permuted myDomain. Then the obj2value will be evaluated
@@ -972,6 +974,13 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete ...
 				assert(numel(values) == numel(gridName2Replace), ...
 					'gridName2Replace and values must be of same size');
 				
+				% set the newDomain once. If obj(1).domain is a quantity.Equidistant domain, it can
+				% not be mixed with other quantity.Domains in an array. Hence, it must be casted to
+				% a quantity.Domain. The following strange form of concatenation an empty Domain
+				% with the required domain, ensures that the result is an array of quantity.Domain
+				% objects.
+				newDomain = [quantity.Domain.empty, obj(1).domain];
+				
 				% here substitution starts:
 				% The first (gridName2Replace{1}, values{1})-pair is
 				% replaced. If there are more cell-elements in those inputs
@@ -1000,7 +1009,6 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete ...
 						% Do not use "return", since, later subs might need to be
 						% called recursively!
 						newValue = obj.on();
-						newDomain = obj(1).domain;
 					elseif any(strcmp(values{1}, obj(1).gridName))
 						% if for a quantity f(z, zeta) this method is
 						% called with subs(f, zeta, z), then g(z) = f(z, z)
@@ -1023,7 +1031,7 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete ...
 							newDomainForOn(all(1:1:numel(newDomainForOn) ~= domainIndices(:)))];
 					else
 						% this is the default case. just grid name is changed.
-						newDomain = obj(1).domain;
+						%newDomain = obj(1).domain;
 						newDomain(obj(1).domain.gridIndex(gridName2Replace{1})) = ...
 							quantity.Domain(values{1}, ...
 							obj(1).domain(obj(1).domain.gridIndex(gridName2Replace{1})).grid);
@@ -1034,7 +1042,6 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete ...
 					% if values{1} is a scalar, then obj is evaluated and
 					% the resulting quantity looses that spatial grid and
 					% gridName
-					newDomain = obj(1).domain;
 					newDomain = newDomain(~strcmp(gridName2Replace{1}, [newDomain.name]));
 					% newGrid is the similar to the original grid, but the
 					% grid of gridName2Replace is removed.
@@ -1049,14 +1056,16 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete ...
 				elseif isnumeric(values{1}) && numel(values{1}) > 1
 					% if values{1} is a double vector, then the grid is
 					% replaced.
-					newDomain = obj(1).domain;
 					newDomain(obj(1).domain.gridIndex(gridName2Replace{1})) = ...
 						quantity.Domain(gridName2Replace{1}, values{1});
 					newValue = obj.on(newDomain);
 				else
 					error('value must specify a gridName or a gridPoint');
-				end
+				end % if ischar(values{1}) || isstring(values{1})
 				if isempty(newDomain)
+					% TODO@Jakob: Is it possible that this case occurrs?
+					% If I see it right, the only case where the newDomain is not set is the case
+					% where a error is thrown.
 					solution = newValue;
 				else
 					solution = quantity.Discrete(newValue, newDomain, ...

+unittests/+quantity/testDiscrete.m

@@ -1546,6 +1546,13 @@ quan4dArbitrary = quan4d.subs({'z', 'zeta', 'eta', 'beta'}, {'zeta', 'beta', 'z'
 testCase.verifyEqual(reshape(quan4d.on({1, 1, 1, 1}), size(quan4d)), ...
 	reshape(quan4dArbitrary.on({1, 1, 1}), size(quan4dAllEta)));
 
+% test a substution where a quantity.EquidistantDomain is used:
+e = quantity.EquidistantDomain("t", 0, 1, "stepSize", 0.1);
+q = Discrete(e);
+p = q.subs(e, "z");
+testCase.verifyEqual( p.domain.name, "z")
+testCase.verifyEqual( on( q.subs(e, z.grid) ), q.on(z.grid) )
+
 
 end