quantity.Discrete.diff: previously, if diff("z", 0) was used, not the 0th...

quantity.Discrete.diff: previously, if diff("z", 0) was used, not the 0th derivative w.r.t. z was calculated but the 1st. This bug is now fixed.

+quantity/Discrete.m

@@ -1326,8 +1326,7 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete ...
 				bMat = flip(bMat, idx(it));
 			end
 			
-			b = quantity.Discrete(bMat, obj(1).domain, ...
-				'name', "flip(" + obj(1).name + ")");
+			b = quantity.Discrete(bMat, obj(1).domain, "name", "flip(" + obj(1).name + ")");
 		end % flipDomain()
 		
 		function newObj = changeDomain(obj, domain)
@@ -2288,7 +2287,13 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete ...
 				diffGridName = {diffGridName.name};
 			end
 			
-			result = obj.diff_inner(k, diffGridName);
+			if k == 0
+				result = obj.copy();
+			elseif k > 0
+				result = obj.diff_inner(k, diffGridName);
+			else
+				error("only defined for derivatives of order k = 0, 1, 2, ...");
+			end
 		end % diff()
 		
 		function I = int(obj, varargin)

+unittests/+quantity/testDiscrete.m

@@ -46,7 +46,7 @@ tc.verifyEqual(testMatrix ./ quan(1).at(0.5), at(testMatrix ./ quan(1), 0.5))
 tc.verifyEqual(at(quan ./ quan, 0.5), ones([2, 2]));
 end
 
-function testiseye(tc)
+function testIseye(tc)
 z = quantity.Domain("z", linspace(0, 1, 11));
 zeta = quantity.Domain("zeta", linspace(0, 1, 11));
 I = quantity.Discrete.eye([2, 3], [z, zeta]);
@@ -59,7 +59,7 @@ I = quantity.Discrete(1+z.grid/100, z);
 tc.verifyFalse(I.iseye());
 I = quantity.Discrete(1+0*z.grid, z);
 tc.verifyTrue(I.iseye());
-end % testEye()
+end % testIseye()
 
 function testSubsDomain(tc)
 z = quantity.Domain("z", linspace(0, 1, 11));
@@ -1021,31 +1021,34 @@ myMat = ones(2, 2) * z.Discrete();
 tc.verifyEqual(myMat.diff.on(), ones(5, 2, 2));
 end % testDiffMat()
 
-function testDiffConstant2d(testCase)
+function testDiffConstant2d(tc)
 %% 2d
 [zNdgrid, zetaNdgrid] = ndgrid(linspace(0, 1, 11), linspace(0, 1, 21));
 myQuantity = quantity.Discrete(cat(3, 2*ones(11, 21), zNdgrid, zetaNdgrid), ...
 	[quantity.Domain("z", linspace(0, 1, 11)), quantity.Domain("zeta", linspace(0, 1, 21))], ...
 	'name', 'constant');
-myQuantityDz = diff(myQuantity, 'z', 1);
-myQuantityDzeta = diff(myQuantity, 'zeta', 1);
+myQuantityDz = diff(myQuantity, "z", 1);
+myQuantityDzeta = diff(myQuantity, "zeta", 1);
+
+% verify zero-th derivative
+tc.verifyEqual( myQuantity.diff("z", 0).on(), myQuantity.on() );
 
-testCase.verifyError( @() diff(myQuantity), ?MException )
-testCase.verifyError( @() diff(myQuantity, 1, {'z', 'zeta'}), ?MException )
-testCase.verifyError( @() diff(myQuantity,  {'z', 'zeta'}), ?MException )
+tc.verifyError( @() diff(myQuantity), ?MException )
+tc.verifyError( @() diff(myQuantity, 1, {'z', 'zeta'}), ?MException )
+tc.verifyError( @() diff(myQuantity,  {'z', 'zeta'}), ?MException )
 
 % constant
-testCase.verifyEqual(myQuantityDz(1).on(), zeros(11, 21));
-testCase.verifyEqual(myQuantityDzeta(1).on(), zeros(11, 21));
+tc.verifyEqual(myQuantityDz(1).on(), zeros(11, 21));
+tc.verifyEqual(myQuantityDzeta(1).on(), zeros(11, 21));
 
 
 % zNdgrid
-testCase.verifyEqual(myQuantityDz(2).on(), ones(11, 21), "AbsTol", 10*eps);
-testCase.verifyEqual(myQuantityDzeta(2).on(), zeros(11, 21), "AbsTol", 10*eps);
+tc.verifyEqual(myQuantityDz(2).on(), ones(11, 21), "AbsTol", 10*eps);
+tc.verifyEqual(myQuantityDzeta(2).on(), zeros(11, 21), "AbsTol", 10*eps);
 
 % zetaNdgrid
-testCase.verifyEqual(myQuantityDz(3).on(), zeros(11, 21), "AbsTol", 10*eps);
-testCase.verifyEqual(myQuantityDzeta(3).on(), ones(11, 21), "AbsTol", 10*eps);
+tc.verifyEqual(myQuantityDz(3).on(), zeros(11, 21), "AbsTol", 10*eps);
+tc.verifyEqual(myQuantityDzeta(3).on(), ones(11, 21), "AbsTol", 10*eps);
 
 end