Problem Statement: I am trying to write MATLAB code for a main caller function (like run_experiment below) to specify which computations I want to execute where computations are made sequentially using other MATLAB functions. Those other functions are to be evaluated based on parameters passed with the main caller function. The said functions used in computations are to be specified with name of the scripts they are written in.
Example Desired Code Behavior: For example, a command like the following should run the preprocess_data, initialise_model and train_model scripts.
>> run_experiment('dataset_1_options', '|preprocess_data|initialise_model|train_model|');
And this command should run only the train_model script but also evaluates its performance:
>> run_experiment('dataset_1_options', '|train_model|evaluate_model|');
In the above examples "|" is used as a delimiter to specify separate function names to be evaluated. Those functions use the options specified with dataset_1_options. Please do not focus on how to separate that part of the input into meaningful function names; I know how to do it with strsplit.
Constraints and Specifications: The function names to be passed as input to the main caller function are NOT anonymous functions. The purpose is to be able to pass such multiple function names as input AND to evaluate them with the options like the above example. They return output to be evaluated in other parts of the research code (i.e. passing data matrices to other functions within the research code as results of the computations carried out within them.)
Question: Given the desired behavior and constraints mentioned above, can anybody help in how to pass the separate function names from another caller function along with options/parameter to those functions? How should the main caller function evaluate the function names passed in as input with the options specified during the call?
Thank you in advance.
You can pass functions to functions in matlab. You just need to use the # sign when you pass it. In your case it would be run_experiment('dataset_1_options', #train_model) inside a script. You could keep your options in a cell array or something. The run_experiment function would just be a regular function,
function [output] = run_experiment(options, train_model, ...);
train_model(options{1}, ...)
.
.
.
end
What you need to do this is create a cell array with your function names and another array with the corresponding options as below
% Function name array
fn_array = {#fn_1, #fn_2, ...};
% Option array
option_array = {{fn1_opt1, fn2opt2, ...}; {fn2_opt1, fn2_opt2, ...};, ...};
These two need to be passed to your run_experiment function which will evaluate them as below
function run_experiment(fn_array, option_array)
num_fn = length(fn_array); %Finds number of functions to evaluate
for ii = 1:num_fn %Evaluates each function
fn_array{ii}(option_array{ii}{:});
end
Related
I created this function to browse all the functions stored in a file and now I want to select my function in my main program how can I select it
This is my function:
function testMode(i)
a=dir('H_*.m');
if exist('i','var')
if isempty(i)
z={a.name}';
[selection,ok]=listdlg('ListString',z,'SelectionMode','single');
if ok
i=find(selection,1,'first');
end
end
nom=a(i).name;
nom=nom(1:end-2);
disp(nom)
else
disp('fonction a un argument')
end
It looks like you will have the name of the function as a string. To call that function, you can either use feval, or you can convert the string to a function handle and call that.
result = feval(nom, argument1);
or
fcn = str2func(nom);
fcn(argument1);
The latter should be preferred, as the conversion can be done once and the function handle re-used after that, and because the calling syntax is exactly the same as calling a regular function.
For more information on function handles, see doc function_handle.
Also, for a different approach, see this document: http://www.mathworks.com/help/matlab/ref/localfunctions.html. If you can create your "menu" of functions as local functions in a single file, this approach could be very clean and simple, as it will directly give you a cell array of function handles of all of those subfunctions. From there, you can get easily get the function name for display using functions command.
Maybe it's a basic question but here I go. I would like to have a .m with all the functions that will be accessed by other scripts and functions.
I tried just doing a script with all the functions and call it in other functions code.
And I got and error. Could you please explain me how can I solve this?
I'm trying this, which gives me no error, and does what I want it to do, still, is it a good way to do it? Any suggestions?
function PruebasLlamaFuncion
funcionFEM=#PruebasTodasFunciones;
a=funcionFEM('OVERPOWER',1,5)
b=funcionFEM('POWEROVERWELMING',2)
end
...
function a=f(nombre,varargin)
f=str2func(nombre)
a=f(varargin{1:end});
end
function d=OVERPOWER(J,c)
d=J*c;
end
function e=POWEROVERWELMING(J)
e=J;
end
Function placement
Matlab, unlike a number of other languages, permits a single file to contain only one main function that is visible to the rest of the system. The main function is the first function. (Documentation)
Any functions that are defined after the main function body are called local functions. These functions each create their own separate workspace (scope) and can be called by one another and, of course, by the main function.
Any functions that are defined within the main function body are called nested functions. These functions have their own workspace but are also able to access and change the variables of their parent function under certain conditions. Nested functions at the same nesting level can call each other and local functions, but local functions cannot call nested functions since they are out of scope.
Workarounds
There are several options available to you depending on how you would like to proceed.
At the risk of giving too many options but desiring to be exhaustive, I'll put the list from what I would do first to what I would do last.
For most things, I would recommend 1 or 2.
The other options are more for creating libraries/APIs, but I included them to show what can be done.
Define Function1 and Function2 in separate m-files on the Matlab path or in the present working directory to call them normally.
Wrap the main body of your work (the one calling the functions) in a function itself and define the other functions as local functions or nested functions. Example:
function output = main(a,b,c)
Result=Function1(a,b,c);
Result2=Function2(b,d);
...
% You can define Function1 and Function2 here for nested functions
end
% Or you can define Function1 and Function2 here for local functions
You can get a bit more fancy and have a function that returns function handles (pointers) to the local or nested functions and then use the (in the example) struct to call the functions in another script:
function Functions = GetFunctions()
Functions.F1 = #(a,b,c) Function1(a,b,c);
Functions.F2 = #(a,b) Function2(a,b);
% You can define Function1 and Function2 here for nested functions
end
% Or you can define Function1 and Function2 here for local functions
If you have R2013b or above, you can do the same thing as above using the localfunctions function to create a cell array of handles to all local functions (in this case, the definitions are required to be outside the main function body).
function Functions = GetFunctions()
Functions = localfunctions(); % R2013b+ only
end
% Define Function1 and Function2 here for local functions
You can also create a class with static functions:
classdef Functions
methods(Static)
% Define Function1 and Function2 here and call them just like the struct above.
end
end
I hope that makes sense and hopefully helps.
I think you're misunderstanding something. A script is for calling a series of functions/other scripts in sequence. If you just want your functions to be accessible in other code, you only need to make sure they're on the path. You would never need a "script containing all the functions". You may be thinking of local functions, but these are the exact opposite of what you want (they can't be called from outside the function where they're defined or other local functions in the same file).
e.g. if Function1 and Function2 are on your path, you could write a script like this, perhaps as a demo for how to use those two functions:
a = 0;
b = 1;
c = 2;
d = 'Unicorns';
Result=Function1(a,b,c);
Result2=Function2(b,d);
It does not and should not have any function definitions in it. If your script can't find the functions, use addpath (see docs), to put the folder where these function files reside into your path. The m files should be given the same name, e.g. the following needs to go in a file called myfunc.m
function result = myfunc(a,b,c)
Functions in your working directory can also be called even if that directory isn't on your path.
I'd like to use the data that are loaded to my workspace in a Matlab function. This is the beginning of my function.
function [totalProfit] = compute(p,exit)
%% Declaration of variables
entry=0;
T = length(data);
.
.
.
end
I'm getting an error:
Undefined function or variable 'data'.
Where is the error?
The variable data was probably defined outside of the function, so it is out of scope.
Pass data as a parameter to compute and then it will be available inside the function.
You can use evalin to work with variables from another workspace. In your example this could be
T = evalin('caller','length(data)')
But please note that in most cases you get cleaner code if you define the variable as input argument for the function. So for your case this would be
function [totalProfit] = compute(p,exit,data)
T = length(data) ;
end
Ran is correct, but I wanted to mention something else. In general, only variables that are passed as arguments to a function are able to be used inside that function, so if you want to use your existing variables inside the function, pass them as input arguments.
It is possible to create global variables which allow you to use them inside functions without passing them as arguments, but it's usually not the best way of writing code. The times where I have used global variables are where I am calling multiple functions from a single script, and I have some constants that will be used by all the functions (for example gravity is a common one). An alternative to global variables is to use a struct, with the variables you want to pass to the function in it, so you only need one extra input argument, but you still have to be a bit careful.
I have written a function to perform permutations of n obejects.
I have the variables a=[1],[2],[3];k=1 and n=4;a contains the objects which are 1,2 and 3 respectively.The following is the function code that i have written:
function [res]=perm(a,k,n,jj)
if k==n
res{jj}=a;
jj=jj+1;
else
for i=k:n
t=a{k};
a{k}=a{i};
a{i}=t;
perm(a,k+1,n,jj)
t=a{k};
a{k}=a{i};
a{i}=t;
end
end
end
However, when i call the function as:
jj=1;
[res]=perm(a,k,n,jj)
I am getting the following error displayed:
Error in ==> perm at 3
if k==n
??? Output argument "res" (and maybe others) not assigned during call to "J:\main
project\perm.m>perm".
Error in ==> mainp at 254
[res]=perm(a,k,n,jj)
The following is the code in the main program with regard to the permutation:
mr=4
for i=1:mr
a{i}=i;
end
n=mr;
%This assignment is for the ease to work with.
%just stored the indices till mr for the purpose of permutation
k=1;
%this is the k that the function perm has
jj=1;
[res]=perm(a,k,n,jj)
Can somebody please help me resolve this?Thanks in advance.
Your else block leaves res undefined.
I think you're assuming that res is a global variable and all invocations of perm will write into different parts of a single cell array. That isn't true. It is an output variable, local to the current call. There's no sharing during recursion, they all have independent cell arrays named res. The parameter jj is also not shared, so adding one is useless as well.
If you want to use this technique of building up the output, you'll need to make sure it is defined at a wider scope than the recursion. For example, use a local helper function:
function [res]=perm(a,k,n,jj)
res = {};
perm_impl(a,k);
function [] = perm_impl(a,k) // doesn't get its own local res, n, or jj
if k==n
res{jj}=a;
jj=jj+1;
else
for i=k:n
t=a{k};
a{k}=a{i};
a{i}=t;
perm_impl(a,k+1)
t=a{k};
a{k}=a{i};
a{i}=t;
end
end
end
end
Now all runs of perm_impl work on the same cell array res, because Matlab documentation says:
Variables within nested functions are accessible to more than just their immediate function. A variable, x, to which you assign a value or use within a nested function resides in the workspace of the outermost function that both contains the nested function and accesses x.
If you intentionally use a variable in this manner, it is not a problem. For examples, see the MATLAB Programming Demo on Nested Functions.
However, if you unintentionally use a variable in this manner, it can result in unexpected behavior. If the highlighting indicates that the scope of a variable spans multiple functions, and that was not your intent, consider:
Renaming the nested function variable so it does not match the outer function variable name.
Passing the variable into the function as an input argument instead of using the variable directly within the nested function
I can't tell whether a was supposed to be shared or not...
I'm trying to define an anonymous function that calls a version of a function that returns multiple outputs.
For example, the function find has two possible output forms:
[row,col] = find(X);
and
[ind] = find(X);
Say I would like to choose the first form inside of an anonymous function.
I have tried
1)
get_columns = #(x) x(2);
and 2)
get_columns = #(x,y) y;
But when I call:
get_columns(find(x))
The first version of get_columns thinks I am calling find as [ind] = find(X) and not as [row,col] = find(X);, while the second one complains with "Not enough input arguments".
Is there a way to trigger a specific output form of a function inside an anonymous function?
Directly, no. Unfortunately, there are a number of features which are inaccessible via anonymous functions, and accessing multiple output arguments is one of them. (The other one I frequently find is that you cannot define an if statement inside an anonymous function. This appears to be a limitation of Matlab syntax more than anything else.
However, a pretty simple helper function can make this possible.
function varargout = get_outputs(fn, ixsOutputs)
output_cell = cell(1,max(ixsOutputs));
[output_cell{:}] = (fn());
varargout = output_cell(ixsOutputs);
This function takes a function handle plus an array of output indexes, and returns the indexed outputs.
If you create this file (hopefully better commented) and put it on your path, then you can access the second output of the find function as by defining the following function
find_2nd = #(x)get_outputs(#()find(x),2)
And now you can find the find the indexes of an array which equal 1 as
>> find_2nd([4 3 2 1]==1)
ans =
4
And now you should be able to access alternative output arguments at-will from within anonymous functions.
This get_outputs function above could be widely useful for brief anonymous functions. Very nice.
Also, regarding the comment that an "if" can't be used in MATLAB, this is only partially true. Identical behavior can easily be implemented anonymously. For instance, here's an anonymous if:
anonymous_if = #(varargin) varargin{2*find([varargin{1:2:end}], 1, 'first')}();
Use:
out = anonymous_if(condition1, action1, condition2, action2, ...);
The action corresponding to the first true condition is executed. For instance, this prints 'hello'.
anonymous_if(false, #() disp('hi'), ... % if false, print 'hi'
true, #() disp('hello')) % else if true, print 'hello'
Granted, it's a bit complicated at first sight, but I keep something like this on my path so I can use an "if" in an anonymous function. Much more complex anonymous functions can be built in this way.