Added plot section to the example file, more detailed description of numeric...

Added plot section to the example file, more detailed description of numeric data access and some minor issues

+quantity/Discrete.m

@@ -1313,6 +1313,7 @@ classdef  (InferiorClasses = {?quantity.Symbolic}) Discrete ...
 			% b(z) = a(1-z) = a.flipDomain('z');
 			% or for the multidimensional case with c(z, zeta)
 			% d(z, zeta) = c(1-z, 1-zeta) = c.flipDomain(["z", "zeta"];
+			% if z and zeta are domains on (0,1).
 			arguments
 				obj
 				myDomainName string

+quantity/example.m

@@ -10,7 +10,7 @@ z = quantity.Domain("z", linspace(0, 1, 101))
 %	"name"	: the name given "z"
 %	"n"		: the number of grid points numel(z.grid) = 101
 %	"lower"	: the lower boundary of z = 0
-%	"upper"	: the upper boundary of z = 0
+%	"upper"	: the upper boundary of z = 1
 
 % Then we can create a(z) = 1 + z using numerical data and this domain z:
 a = quantity.Discrete(...
@@ -23,23 +23,31 @@ a = quantity.Discrete(...
 % verify that a(z) is the desired variable by plotting it:
 a.plot();
 
-%% Access to numerical data using the method on()
-% verify that a(z) = 1 + z by evaluating it for different points in z = 0, 0.5, 1:
-[a.on(0), a.on(0.5), a.on(1)]
-% or more compact:
-a.on([0, 0.5, 1])
-
-% on(gridValues) performs an interpolation, when the specified values do not lie on
-%  the grid a.grid, for instance
-a.on(0.1234567123123123);
-
-% on() without any input arguments returns the original data, 
+%% Access to numerical data
+% to access the numerical three methods are provided:
+% The first is the method a.on(). If it is called without an argument it returns the original data:
 isequal(a.on(), 1+z.grid);
-
 % additionally, on can be called using quantity.Domain objects. Sampling a with 3 discrete points:
 zSample = quantity.Domain("z", linspace(0, 1, 3)); % the new domain must have the same name as the 
 		% domain of a.
 a.on(zSample)
+% on(gridValues) performs an interpolation, when the specified values do not lie on
+%  the grid a.grid, for instance
+a.on(0.1234567123123123);
+
+% the second method to access the numeric data is to use the "at" method:
+a.at(0)
+% only single points can be specified. This is advantangeous if a would be a matrix valued function.
+
+% verify that a(z) = 1 + z by evaluating it for different points in z = 0, 0.5, 1:
+[a.at(0), a.at(0.5), a.at(1)]
+% or more compact:
+a.on([0, 0.5, 1])
+
+% the third method to access the numeric data is to use the index. Evaluation of the first and the
+% last point would be:
+a.atIndex(1)
+a.atIndex(end)
 
 %% Lets do some basic math operations
 % spatial derivatives
@@ -51,10 +59,10 @@ plot([a; a_dz; a_dzz]);	% note: as the derivative is implemented numerically usi
 						%	gradient method, numerical errors occur.
 % plus and minus
 aPlus1 = a + 1;
-TwoMinusA = 2-a;
+twoMinusA = 2-a;
 
 % note that quantites can be concatenated using [ ... ] or the methods vertcat, horzcat or cat.
-aaa = [a; aPlus1; TwoMinusA];
+aaa = [a; aPlus1; twoMinusA];
 plot(aaa);
 
 %% Sustitution: b = a(zeta)
@@ -93,6 +101,12 @@ misc.subsurf(cDisc, "xLabel", "z", "yLabel", "\zeta", "myTitle", "c");
 % the second dimension j should represent z, this can be achieved using the domains:
 cDisc = c.on([zetaSample, zSample]);
 
+% to evaluate a function c(z,zeta) pointwise
+z1 = 0.19;
+zeta1 = 0.29;
+c.at({z1, zeta1})
+%can be used
+
 %% Substitution: of multidimensional data c(z, zeta)
 % use subs to replace variables z or zeta with a constant value, for instance,
 % c2(zeta) = c(0.25, zeta)
@@ -145,6 +159,25 @@ y = x + cumInt(K*x.subs("z", "zeta"), "zeta", 0, "z");
 %			4. input: upper bound of integral 'z'
 y.plot();
 
+%% plotting of quantities
+% As have been shown, quantities can be displayed by the plot method. For each quantity a new window
+% is opened and each entry of a matrix valued quantity is plotted into a own subplot. To specifiy
+% which figure should be used for a plot the optional name-value-pair argument "fig" can be used:
+a.plot("fig", 1)
+% will plot quantity a into figure 1. If a second quantity should be plotted into the same window,
+% the optional name-value-pair "hold" can be used:
+a_dz.plot("fig", 1, "hold", true)
+% will plot first derivative of a into the same figure. 
+% To use the subplot to display different quantities, use the "currentFigure" optional
+% name-value-argument:
+figure(1); clf;
+subplot(211);
+c.plot("currentFigure", true);
+% with this argument combined with the "hold" option, all entries of a matrix valued quantity can be
+% composed into one axis:
+subplot(212);
+aaa.plot("currentFigure", true, "hold", true)
+
 %% Commonly used methods
 % Similar to many matlab built-in methods the following operations are supported:
 % - math opertions: mtimes, inv, exp, expm, log, log10, sqrt, sqrtm, uminus, prod, sum, power, ...