Here is my code:
f.m:
classdef f < handle
properties (Access = public)
functionString = '';
x;
end
methods
function obj = f
if nargin == 0
syms s;
obj.x = input('Enter your function: ');
obj.functionString = ilaplace(obj.x);
end
end
function value = subsref(obj, a)
t = a.subs{:};
value = eval(obj.functionString);
end
function display(obj)
end
end
end
test.m:
syms s t;
[n d] = numden(f.x); % Here I want to use x, which is the user input, How can I do such thing?
zeros = solve(n);
poles = solve(d);
disp('The Poles:');
disp(poles);
disp('The Zeros:');
disp(zeros);
disp('The Result:');
disp(z(t));
disp('The Initial Value:');
disp(z(0));
disp('The Final Value:');
disp(z(Inf));
When I type test in the command window, it tells me the following:
>> test
??? The property 'x' in class 'f' must be accessed from a class instance because it
is not a Constant property.
As Alex points out, you need an instance of f to access the member property x, like so:
myf = f();
f.x
You do not need an accessor method to get at x as it is defined as a public property. If you chose to make x private, then you'd need an accessor method something like this:
function x = getX( obj )
x = obj.x;
end
Related
I have several properties that use essentially the same set method:
classdef MyClass
properties
A
B
end
methods
function mc = MyClass(a,b) % Constructor
mc.A = a;
mc.B = b;
end
function mc = set.A(mc, a) % setter for A
if a > 5
mc.A = a;
else
error('A should be larger than 5');
end
end
function mc = set.B(mc, b) %setter for B
if b > 5
mc.B = b;
else
error('B should be larger than 5');
end
end
end
end
Is there a way to use only one set function for variables A and B? (Please note that the error function use the property names as strings.)
Is it suggested to use only one set function? What are the possible drawbacks of using one set function?
The only real way is to extract the common code to another function, and call it from the setters:
classdef MyClass
properties
A
B
end%public properties
methods
function mc = MyClass(a,b) % Constructor
mc.A = a;
mc.B = b;
end
function mc = set.A(mc, value) % setter for A
mc = mc.commonSetter(value, 'A');
end
function mc = set.B(mc, value) %setter for B
mc = mc.commonSetter(value, 'B');
end
end%public methods
methods(protected = true)
function mc = commonSetter(mc, property, value)
if value <= 5;
error([property ' should be less than 5');
end
mc.(property) = value;
end%commonSetter()
end%protected methods
end%classdef
The very first one in this documentation:
http://www.mathworks.com/help/matlab/matlab_oop/getting-familiar-with-classes.html
The class is:
classdef BasicClass
properties
Value
end
methods
function r = roundOff(obj)
r = round([obj.Value],2);
end
function r = multiplyBy(obj,n)
r = [obj.Value] * n;
end
end
end
When I run it this way
a = BasicClass
a.Value = pi/3;
It works fine and does what it should but this piece of code
a = BasicClass(pi/3);
Gives the following error:
"Error using round
Too many input arguments."
What does it mean? (I'm using R2014a) Is it stupid to use oop in Matlab? LOL
Your error message doesn't look correct compared with the code, whichever your missing a class constructor (as is mentioned at the half way down the help link):
classdef BasicClass
properties
Value
end
methods
% Class constructor -> which you can pass pi/3 into.
function obj = BasicClass ( varargin )
if nargin == 1
obj.Value = varargin{1};
end
end
% Your Methods
function r = roundOff(obj)
r = round([obj.Value],2);
end
function r = multiplyBy(obj,n)
r = [obj.Value] * n;
end
end
end
I have a class in MATLAB that represents an imaginary number. I have a constructor and two data members: real and imag. I am playing with overloading operator in a class and I want to make it work with matrices:
function obj = plus(o1, o2)
if (any(size(o1) ~= size(o2)))
error('dimensions must match');
end
[n,m] = size(o1);
obj(n,m) = mycomplex();
for i=1:n
for j=1:m
obj(i,j).real = o1(i,j).real + o2(i,j).real;
obj(i,j).imag = o1(i,j).imag + o2(i,j).imag;
end
end
end
But I don't want to use for loops. I want to do something like:
[obj.real] = [o1.real] + [o2.real]
But I don't understand why it does not work... the error says:
"Error in + Too many output arguments".
I know that in MATLAB it is good to avoid for loops for speed up... Can someone explain me why this does not work, and the right way to think about vectorization in MATLAB with an example for my function?
Thanks in advance.
EDIT: definition of my complex class:
classdef mycomplex < handle & matlab.mixin.CustomDisplay
properties (Access = public)
real;
imag;
end
methods (Access = public)
function this = mycomplex(varargin)
switch (nargin)
case 0
this.real = 0;
this.imag = 0;
case 1
this.real = varargin{1};
this.imag = 0;
case 2
this.real = varargin{1};
this.imag = varargin{2};
otherwise
error('Can''t have more than two arguments');
end
obj = this;
end
end
end
Consider the implementation below. First some notes:
the constructor can be called with no parameters. This is important to allow preallocating object arrays: obj(m,n) = MyComplex()
for convenience, the constructor accepts either scalar of array arguments. So we can call: c_scalar = MyComplex(1,1) or c_array = MyComplex(rand(3,1), rand(3,1))
the plus operator uses a for-loop for now (we will later change this).
(Note that I skipped some validations in the code, like checking that o1 and o2 are of the same size, similarly for a and b in the constructor).
classdef MyComplex < handle
properties
real
imag
end
methods
function obj = MyComplex(a,b)
% default values
if nargin < 2, b = 0; end
if nargin < 1, a = 0; end
% accepts scalar/array inputs
if isscalar(a) && isscalar(b)
obj.real = a;
obj.imag = b;
else
[m,n] = size(a);
obj(m,n) = MyComplex();
for i=1:m*n
obj(i).real = a(i);
obj(i).imag = b(i);
end
end
end
function obj = plus(o1, o2)
[m,n] = size(o1);
obj(m,n) = MyComplex(); % preallocate object array
for i=1:m*n % linear indexing
obj(i).real = o1(i).real + o2(i).real;
obj(i).imag = o1(i).imag + o2(i).imag;
end
end
end
end
An example of using the class:
% scalar objects
>> c1 = MyComplex(1,2);
>> c2 = MyComplex(3,4);
>> c3 = c1 + c2
c3 =
MyComplex with properties:
real: 4
imag: 6
% array of objects
>> c4 = [c1;c1] + [c2;c2]
c4 =
2x1 MyComplex array with properties:
real
imag
Now here is a vectorized version of the plus method:
function obj = plus(o1, o2)
[m,n] = size(o1);
obj(m,n) = MyComplex();
x = num2cell([o1.real] + [o2.real]);
[obj.real] = deal(x{:});
x = num2cell([o1.imag] + [o2.imag]);
[obj.imag] = deal(x{:});
end
I'm using the syntax: [objarray.propName] to reference a property in object arrays, this return the values as a vector.
For the opposite of assigning a property in an object array, I use comma-separated lists, thus I had to convert to a cell array to get the x{:} convenient syntax.
Note that the deal call is not strictly needed, we could write the assignment without it:
[obj.real] = x{:};
The line obj(n,m) = mycomplex() looks very suspicious. I think what you want to do there is obj = mycomplex(n,m) instead.
I can't see the rest of your code, but it's miraculous to me that this line even works. I suspect that you have an obj variable stored somewhere already, and this code simply overwrites one entry of that variable. I predict that if you clear all variables, it's going to fail on that line.
Again, it's very difficult to understand what happens without knowing what mycomplex() actually does.
Is there a built-in way to automatically propagate the nargout of a calling function to the called function? (Or some for a called function to figure out the nargout of the calling function?)
For example, say that
% foo.m
function [X, Y] = foo()
[X, Y] = bar();
end
and
% bar.m
function [X, Y] = bar()
X = 1;
if upstream_nargout() < 2
Y = 0;
else
Y = big_nasty_time_consuming_monster();
end
end
Of course, one could always define foo like this
% foo.m
function [X, Y] = foo()
if nargout < 2
X = bar();
else
[X, Y] = bar();
end
end
...or define bar with an extra argument to carry the caller's nargout, but I'm wondering if there's a reasonable way to achieve the same effect without resorting to this.
varargout and nargout works as follows:
% foo.m
function varargout = foo()
[varargout{1:nargout}] = bar();
end
% bar.m
function varargout = bar()
varargout{1} = 1;
if nargout > 1,
fprintf('bar: computing second output\n');
varargout{2} = rand(); % OR big_nasty_time_consuming_monster();
end
end
Then:
>> X = foo
X =
1
>> [X,Y] = foo
bar: computing second output
X =
1
Y =
0.5647
NOTE: The version of foo in the question following "Of course, one could always define foo like this" would certainly work, but this alternative allows you to have a single line in foo calling bar, rather than another if/else. That was the point of the question as I read it.
I don't see any reason to propagate the callers nargout, this should match your requirements:
function [X, Y] = foo()
if nargout < 2
X = bar();
else
[X, Y] = bar();
end
end
.
function [X, Y] = bar()
X = 1;
if nargout < 2
Y = 0;
else
Y = big_nasty_time_consuming_monster();
end
end
If you really need the calles nargout use evalin('caller','nargout'), but I would never combine nargin/nargout with evalin('caller', you can easily produce code which is impossible to debug.
In a class with the dependent property c, I would like to call c's setter with a third argument that equals 'a' or 'b', choosing which independent property to alter in order to set c.
The code is
classdef test < handle
properties
a
b
end
properties (Dependent = true)
c
end
methods
function c = get.c(obj)
c = obj.a + obj.b;
end
function obj = set.c(obj, value, varargin)
if(nargin == 2)
obj.a = value - obj.b;
end
if(nargin == 3 && argin(3) == 'a') % how do I enter this loop?
obj.a = value - obj.b;
end
if(nargin == 3 && argin(3) == 'b') % or this?
obj.b = value - obj.a;
end
end
end
end
This call works:
myobject.c = 5
But how do I call the setter with a third parameter equaling 'a' or 'b'?
You can't. set always accepts only two arguments. You could work around it with an additional dependent property:
classdef test < handle
properties
a
b
end
properties (Dependent = true)
c
d
end
methods
function c = get.c(obj)
c = obj.a + obj.b;
end
function d = get.d(obj)
d = c;
end
function obj = set.c(obj, value)
obj.a = value - obj.b;
end
function obj = set.d(obj, value)
obj.b = value - obj.a;
end
end
end
or by choosing a different syntax and/or approach:
myObject.set_c(5,'a') %// easiest; just use a function
myObject.c = {5, 'b'} %// easy; error-checking will be the majority of the code
myObject.c('a') = 5 %// hard; override subsref/subsasgn; good luck with that
or something else creative :)