I want to know If it's possible and how, to hide some parts of a line or whole lines of code from a script in MATLAB. For example:
if a=b
x=y+1; x=x^2;
end
And have the x=x^2 hidden, but still run the process. I mean:
if a=b
x=y+1;
end
(wringing hands with evil grin on face)
If you really want to mess with people like this, you're going to want to go down the operator overloading route. Come with me on a journey where you will almost certainly shoot yourself in the foot while trying to play a joke on someone else!
(lightning crackles over the laughter of a madman)
I've discussed this in a few other questions before (here and here). Basically, you can change the default behavior of built-in operators for MATLAB data types. In this case, we'll change how the plus operator works for variables of class double (the default variable type). Make a folder called #double on your MATLAB path, then create a file called plus.m and put the following code inside it:
function C = plus(A, B)
C = builtin('plus', A, B);
if strcmp(inputname(1), 'y')
C = C.^2;
end
end
Now, try it for yourself...
>> y=1; % Initialize y
>> x=y+1
x =
4 % Wait a minute...
>> x=1+1
x =
2 % OK
>> x=1+y
x =
2 % OK
>> x=y+1
x =
4 % What?!
>> x=y+2;
x =
9 % No!!
>> y=3;
>> x=y+1
x =
16 % Oh noes! I've been hax0red!!11!1!
How it works:
The new plus function shadows the built-in one, so it gets called when performing addition on doubles. It first invokes the built-in plus to do the actual addition using the builtin function. This is necessary, because if you wrote C=A+B; here it would call the phony plus again and cause infinite recursion. Then, it uses the inputname function to check what the variable name of the first input to the function is. If it's 'y', we square the result before returning it.
Have fun!!!
...and remember to remove it when you're done. ;)
if a==b
x = y+1;
for ind = 1
x = x^2;
end
end
Bit of a wacky way, but you can collapse loop/end blocks like for and while loops. Simply click the - sign in the editor:
So for two or less lines this doesn't help you, but if you want to hide e.g. 40 lines, it shortens it appreciably.
Another option is to simply chuck in a hundred or so spaces and make it obfuscated:
if a==b
x = y+1; x = x^2;
end
Thanks to excaza the most obfuscated way of all to write x=x^2;:
eval(cast((sscanf('240,122,240,188,100,118', '%d,')./2)', 'like', ''))
Related
Is it possible to get the 'nth' return value from a function without having to create dummy variables for all n-1 return values before it?
Let's say, I have the following function in MATLAB:
function [a,b,c,d] = func()
a = 1;
b = 2;
c = 3;
d = 4;
Now suppose, I'm only interested in the third return value. This can be accomplished by creating one dummy variable:
[dummy, dummy, variableThatIWillUse, dummy] = func;
clear dummy;
But I think this is kind of ugly. I would think that you might be able to do something like one of the following things, but you can't:
[_, _, variableThatIWillUse, _] = func;
[, , variableThatIWillUse, ] = func;
variableThatIWillUse = func(3);
variableThatIWillUse = func()(3);
Are there any elegant ways to do this that do work?
So far, the best solution is to simply use the variableThatIWillUse as a dummy variable. This saves me from having to create a real dummy variable that pollutes the work-space (or that I would need to clear). In short: the solution is to use the variableThatIWillUse for every return value up until the interesting one. Return values after can simply be ignored:
[variableThatIWillUse, variableThatIWillUse, variableThatIWillUse] = func;
I still think this is very ugly code.
With MATLAB Version 7.9 (R2009b) you can use a ~, e.g.,
[~, ~, variableThatIWillUse] = myFunction();
Note that the , isn't optional. Just typing [~ ~ var] will not work, and will throw an error.
See the release notes for details.
This is somewhat of a hack, but it works:
First a quick example function:
Func3 = #() deal(1,2,3);
[a,b,c]=Func3();
% yields a=1, b=2, c=3
Now the key here is that if you use a variable twice on the left-hand side of a multiple-expression assignment, an earlier assignment is clobbered by the later assignment:
[b,b,c]=Func3();
% yields b=2, c=3
[c,c,c]=Func3();
% yields c=3
(Just to check, I also verified that this technique works with [mu,mu,mu]=polyfit(x,y,n) if all you care about from polyfit is the third argument.)
There's a better approach; see ManWithSleeve's answer instead.
If you wish to use a style where a variable will be left to fall into the bit bucket, then a reasonable alternative is
[ans, ans, variableThatIWillUse] = myfun(inputs);
ans is of course the default junk variable for MATLAB, getting overwritten often in the course of a session.
While I do like the new trick that MATLAB now allows, using a ~ to designate an ignored return variable, this is a problem for backwards compatibility, in that users of older releases will be unable to use your code.
I generally avoid using new things like that until at least a few MATLAB releases have been issued to ensure there will be very few users left in the lurch. For example, even now I find people are still using an old enough MATLAB release that they cannot use anonymous functions.
Here's another option you can use. First make a cell array to capture all the outputs (you can use the NARGOUT function to determine how many outputs a given function returns):
a = cell(1,3); % For capturing 3 outputs
% OR...
a = cell(1,nargout(#func)); % For capturing all outputs from "func"
Then call the function as follows:
[a{:}] = func();
Then simply remove the element from a that you want, and overwrite a:
a = a{3}; % Get the third output
I wrote a kth out function:
function kth = kthout(k, ffnc, varargin)
% kthout: take the kth varargout from a func call %FOLDUP
%
% kth = kthout(k, ffnc, varargin)
%
% input:
% k which varargout to get
% ffnc function to call;
% varargin passed to ffnc;
% output:
% kth the kth argout;
[outargs{1:k}] = feval(ffnc, varargin{:});
kth = outargs{k};
end %function
You can then call
val_i_want = kthout(3, #myfunc, func_input_1, func_input_2);
You could also wrap up the function like:
func_i_want = #(varargin)(kthout(3, #myfunc,varargin{:})); % Assuming you want the third output.
After which you use
val_i_want = func_i_want(func_input_1, func_input_2);
Note that there is overhead associated with using anonymous functions like this, and this is not something I would do in code that would be called thousands of times.
In MATLAB 2010a, I found a neat way of doing what you are asking for.
It is simply to use the character "~" (without the quotes of course) as your dummy variable (as many as you want when returning multiple parameters). This also works for input parameters to functions if the functions are designed to handle missing data.
I don't know if this existed in previous versions, but I just came across it recently.
You can make a function (or anonymous function) that only returns selected outputs, e.g.
select = #(a,b) a(b);
Then you can call your function like this:
select(func,2);
select(func,1:3);
Or you can assign the output to a variable:
output(1,2:4) = select(func,1:3);
I don't see any reason not to use ans(n). Like this:
size(rand([5 10 20 40]));
b = ans(2);
It gives b = 10, and this way would be compatible with all MATLAB versions. Note that size() here is just used to represent any function that has multiple return variables.
Furthermore, this works to get the second output argument when you don't know how many arguments there will be! Whereas, if you do this:
[~, b] = size(a);
Then b = 8000! (You need to end with ~, to catch more arguments!)
total newbie here. I'm having problems looping a function that I've created. I'm having some problems copying the code over but I'll give a general idea of it:
function[X]=Test(A,B,C,D)
other parts of the code
.
.
.
X = linsolve(K,L)
end
where K,L are other matrices I derived from the 4 variables A,B,C,D
The problem is whenever I execute the function Test(1,2,3,4), I can only get one answer out. I'm trying to loop this process for one variable, keep the other 3 variables constant.
For example, I want to get answers for A = 1:10, while B = 2, C = 3, D = 4
I've tried the following method and they did not work:
Function[X] = Test(A,B,C,D)
for A = 1:10
other parts of the code...
X=linsolve(K,L)
end
Whenever I keyed in the command Test(1,2,3,4), it only gave me the output of Test(10,2,3,4)
Then I read somewhere that you have to call the function from somewhere else, so I edited the Test function to be Function[X] = Test(B,C,D) and left A out where it can be assigned in another script eg:
global A
for A = 1:10
Test(A,2,3,4)
end
But this gives an error as well, as Test function requires A to be defined. As such I'm a little lost and can't seem to find any information on how can this be done. Would appreciate all the help I can get.
Cheers guys
I think this is what you're looking for:
A=1:10; B=2; C=3; D=4;
%Do pre-allocation for X according to the dimensions of your output
for iter = 1:length(A)
X(:,:,iter)= Test(A(iter),B,C,D);
end
X
where
function [X]=Test(A,B,C,D)
%other parts of the code
X = linsolve(K,L)
end
Try this:
function X = Test(A,B,C,D)
% allocate output (it is faster than changing the size in every loop)
X = {};
% loop for each position in A
for i = 1:numel(A);
%in the other parts you have to use A(i) instead of just A
... other parts of code
%overwrite the value in X at position i
X{i} = linsolve(K,L);
end
end
and run it with Test(1:10,2,3,4)
To answer what went wrong before:
When you loop with 'for A=1:10' you overwrite the A that was passed to the function (so the function will ignore the A that you passed it) and in each loop you overwrite the X calculated in the previous loop (that is why you can only see the answer for A=10).
The second try should work if you have created a file named Test.m with the function X = (A,B,C,D) as the first code in the file. Although the global assignment is unnecessary. In fact I would strongly recommend you not to use global variables as it gets very messy very fast.
total_Route = zeros(4,4);
tmp = evalin('base', 't'); % i initialise t in the Workspace with the value 1
if(tmp==5)
tmp=1;
end
total_Route(tmp,1) = Distance_Traveled_CM;
total_Route(tmp,2) = Hauptantrieb_Verbrauchte_Energie_CM;
total_Route(tmp,3) = Nebenaggregate_Verbrauch_Real_CM;
total_Route(tmp,4) = t;
Total_Distance_Traveled_CM = sum(total_Route(:,1));
set(handles.edit3, 'string',Total_Distance_Traveled_CM);
Total_Hauptantrieb_Verbrauchte_Energie_CM = sum(total_Route(:,2));
set(handles.edit4, 'string',Total_Hauptantrieb_Verbrauchte_Energie_CM);
Total_Nebenaggregate_Verbrauch_Real_CM = sum(total_Route(:,3));
set(handles.edit5, 'string',Total_Nebenaggregate_Verbrauch_Real_CM);
%% Index
set(handles.edit15, 'string',tmp);
assignin('base', 't', tmp + 1); % with this line i can increment "t" after each pass
guidata(hObject,handles);
Sorry that I did not explain my problem well.
#Sardar_Usama I want to run the loop only once but t should be incremented after each time I click on my Button.
# Sembei Norimaki end is at the end of my codes, have forgotten to write it in my question
#Patrik & #Dennis Jaheruddin let me explain my problem again
I created a Matrix with 4×4 Elements with the Goal to save the results of each my Variable (Total_Distance_Traveled_CM, Total_Hauptantrieb_Verbrauchte_Energie_CM etc...) after each Simulation in the element of my Matrix (See image below).
I want by pressing a button (on my GUI) to get always the sum of each Column.
Example
The first pass: t = 1--> Distance_Traveled(1,1) is 900 the GUI will take through clicking on the Button, the sum of the first column (which is 900+0+0+0) and write it in a static test.
The second pass t = 2--> Distance_traveled(2,1) is 800 the GUI will take the sum of the first column (which is 900+800+0+0) and write it in a static test and the same thing should happen with the other column.
This should continue until t = 4 i.e. until it does the same thing for each column, then it should reset.
I hope, I have explained my problem better this time and I apologize for my bad English.
I appreciate any help.
Based on your code fragment the for loop is only called once.
However, the contents of the for loop are ran for four times. (first for i=1 then for 1=2 etc..)
If you only want to run one of these options the solution is very simple:
i = 1
yourLoopContent
If i is always 0 the first time, and you always want to run it for the current i, it would also be simple:
yourLoopContent
i = i+1;
However if i may not be set properly the first time, things get messy. This is because i is by default defined as the square root of minus 1.
Therefore I would recommend you to use a different letter like t instead. Then you could do this:
if ~exists(t)
t=0;
end
yourLoopContent %Everywhere using t instead of i
t = t+1;
In general you may want to avoid i as an index to stay clear of complex number issues.
I'm not sure if I got your question correctly, but it seems to me that what you look for is a cumulative sum. This can be done either buy summing on 1:t or by using cumsum. I'm not sure why you use a loop, but if this is only for the summing then cumsum can replace that.
Here is some example in your code:
total_Route = zeros(4,4);
% I commented below what is not part of the question
for t = 1:4
total_Route(t,:) = [Distance_Traveled_CM,
Hauptantrieb_Verbrauchte_Energie_CM,
Nebenaggregate_Verbrauch_Real_CM,
t];
% the following line compute the comulative sum from the top of each
% column to every element in it, so cs_total_Route(3,2) is like
% sum(total_Route(1:3,2)):
cs_total_Route = cumsum(total_Route);
Total_Distance_Traveled_CM = cs_total_Route(t,1); % OR sum(total_Route(1:t,1))
% set(handles.edit3, 'string',Total_Distance_Traveled_CM);
Total_Hauptantrieb_Verbrauchte_Energie_CM = cs_total_Route(t,2); % OR sum(total_Route(1:t,2))
% set(handles.edit4, 'string',Total_Hauptantrieb_Verbrauchte_Energie_CM);
Total_Nebenaggregate_Verbrauch_Real_CM = cs_total_Route(t,3); % OR sum(total_Route(1:t,3))
% set(handles.edit5, 'string',Total_Nebenaggregate_Verbrauch_Real_CM);
% set(handles.edit15, 'string',t);
end
And here is a quick look on what cumsum does (with some random numbers for total_Route):
total_Route =
671 4.6012 1.0662 1
840 3.6475 0.58918 2
354 8.6056 2.1313 3
893 4.1362 2.0118 4
cs_total_Route =
671 4.6012 1.0662 1
1511 8.2487 1.6554 3
1865 16.854 3.7867 6
2758 20.991 5.7985 10
Is this what you looked for?
I have a simple but interesting question. i tired hard to google it but my google got upset and giving me the same results...
i wanted to know is it possible to Update a constant variable form workspace command..
A Simple Example:
function y =StupidQuestion
a = 10; % some value
b =[5,6,7;1,2,8]; % some value
y = b*a % some operation
I forget to tell you that we can do it with simulink block by using below command
set_param('obj', 'parameter1', value1, 'parameter2', value2, ...)
i Want to use the assigned value for 3 weeks and without any reason i wants to change my values [a,b] to other but through command windows. any Idea. Waiting for your interesting Reply...................
You can set defaults for the inputs:
function y = foo(a,b)
if nargin < 1 || isempty(a), a = 10; end
if nargin < 2 || isempty(b), b = [5,6,7;1,2,8]; end
y = b*a
end
You can call foo() without inputs (and it will use the defaults for a and b) or supply your own values as: foo(12), foo(12,[10,20]), foo([],[23,23]), etc...
A possible way is to save some variables in an external file. Note that in this case a and b are only in the function workspace (you won't see their values unless you load the contents of test.mat separately). I'm passing the filename in rather than hard-coding it in case you need to switch between multiple settings.
Personally I would prefer to have a human-readable data file, but the concept remains the same (you'd just need some parser function which returned values for a and b given a file).
a = 10; % some value
b =[5,6,7;1,2,8]; % some value
save('test.mat','a','b');
clear a b;
function y = savedvariables(filename)
load(filename);
y = b*a; % some operation
end
y = savedvariables('test.mat');
Is it possible to get the 'nth' return value from a function without having to create dummy variables for all n-1 return values before it?
Let's say, I have the following function in MATLAB:
function [a,b,c,d] = func()
a = 1;
b = 2;
c = 3;
d = 4;
Now suppose, I'm only interested in the third return value. This can be accomplished by creating one dummy variable:
[dummy, dummy, variableThatIWillUse, dummy] = func;
clear dummy;
But I think this is kind of ugly. I would think that you might be able to do something like one of the following things, but you can't:
[_, _, variableThatIWillUse, _] = func;
[, , variableThatIWillUse, ] = func;
variableThatIWillUse = func(3);
variableThatIWillUse = func()(3);
Are there any elegant ways to do this that do work?
So far, the best solution is to simply use the variableThatIWillUse as a dummy variable. This saves me from having to create a real dummy variable that pollutes the work-space (or that I would need to clear). In short: the solution is to use the variableThatIWillUse for every return value up until the interesting one. Return values after can simply be ignored:
[variableThatIWillUse, variableThatIWillUse, variableThatIWillUse] = func;
I still think this is very ugly code.
With MATLAB Version 7.9 (R2009b) you can use a ~, e.g.,
[~, ~, variableThatIWillUse] = myFunction();
Note that the , isn't optional. Just typing [~ ~ var] will not work, and will throw an error.
See the release notes for details.
This is somewhat of a hack, but it works:
First a quick example function:
Func3 = #() deal(1,2,3);
[a,b,c]=Func3();
% yields a=1, b=2, c=3
Now the key here is that if you use a variable twice on the left-hand side of a multiple-expression assignment, an earlier assignment is clobbered by the later assignment:
[b,b,c]=Func3();
% yields b=2, c=3
[c,c,c]=Func3();
% yields c=3
(Just to check, I also verified that this technique works with [mu,mu,mu]=polyfit(x,y,n) if all you care about from polyfit is the third argument.)
There's a better approach; see ManWithSleeve's answer instead.
If you wish to use a style where a variable will be left to fall into the bit bucket, then a reasonable alternative is
[ans, ans, variableThatIWillUse] = myfun(inputs);
ans is of course the default junk variable for MATLAB, getting overwritten often in the course of a session.
While I do like the new trick that MATLAB now allows, using a ~ to designate an ignored return variable, this is a problem for backwards compatibility, in that users of older releases will be unable to use your code.
I generally avoid using new things like that until at least a few MATLAB releases have been issued to ensure there will be very few users left in the lurch. For example, even now I find people are still using an old enough MATLAB release that they cannot use anonymous functions.
Here's another option you can use. First make a cell array to capture all the outputs (you can use the NARGOUT function to determine how many outputs a given function returns):
a = cell(1,3); % For capturing 3 outputs
% OR...
a = cell(1,nargout(#func)); % For capturing all outputs from "func"
Then call the function as follows:
[a{:}] = func();
Then simply remove the element from a that you want, and overwrite a:
a = a{3}; % Get the third output
I wrote a kth out function:
function kth = kthout(k, ffnc, varargin)
% kthout: take the kth varargout from a func call %FOLDUP
%
% kth = kthout(k, ffnc, varargin)
%
% input:
% k which varargout to get
% ffnc function to call;
% varargin passed to ffnc;
% output:
% kth the kth argout;
[outargs{1:k}] = feval(ffnc, varargin{:});
kth = outargs{k};
end %function
You can then call
val_i_want = kthout(3, #myfunc, func_input_1, func_input_2);
You could also wrap up the function like:
func_i_want = #(varargin)(kthout(3, #myfunc,varargin{:})); % Assuming you want the third output.
After which you use
val_i_want = func_i_want(func_input_1, func_input_2);
Note that there is overhead associated with using anonymous functions like this, and this is not something I would do in code that would be called thousands of times.
In MATLAB 2010a, I found a neat way of doing what you are asking for.
It is simply to use the character "~" (without the quotes of course) as your dummy variable (as many as you want when returning multiple parameters). This also works for input parameters to functions if the functions are designed to handle missing data.
I don't know if this existed in previous versions, but I just came across it recently.
You can make a function (or anonymous function) that only returns selected outputs, e.g.
select = #(a,b) a(b);
Then you can call your function like this:
select(func,2);
select(func,1:3);
Or you can assign the output to a variable:
output(1,2:4) = select(func,1:3);
I don't see any reason not to use ans(n). Like this:
size(rand([5 10 20 40]));
b = ans(2);
It gives b = 10, and this way would be compatible with all MATLAB versions. Note that size() here is just used to represent any function that has multiple return variables.
Furthermore, this works to get the second output argument when you don't know how many arguments there will be! Whereas, if you do this:
[~, b] = size(a);
Then b = 8000! (You need to end with ~, to catch more arguments!)