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I use the symbolic toolbox in matlab to generate some very long symbolic expressions. Then I use matlabFunction to generate a function file.
Say there are three parameters: p1, p2 and p3.
I have a cell with strings {'p1', 'p2', 'p3'}.
In the derivation of the model I generate symbolic variables p1, p2 and p3 out of them using eval in a loop and stack them in a vector par.
Then when in matlabFunction, I specify par as input.
Moreover, I save the cell string in a .mat file.
Then when I want to simulate this model, I can construct this parameter array using that cell of strings from the .mat file out of 30 available parameters and their values.
Advantages: No need to keep track of the different parameters if I add one to . I can change the order, mess around, but older models still work.
Disadvantage:
Turning things into a function file leads to this error (psi is one of the parameters):
Error: File: f_derive_model.m Line: 96 Column: 5
"psi" previously appeared to be used as a function or
command, conflicting with its use here as the name of a
variable.
A possible cause of this error is that you forgot to
initialize the variable, or you have initialized it
implicitly using load or eval.
Apparently some unnescescary checking is going on because the variable will be intialized in an eval statement.
Question: How can I avoid eval but keep the list of parameters indepent from the model stuff.
Code deriving the long equations:
% Model parameters
mdl.parameters = {'mp','mb','lp','lb','g','d','mP','mM','k','kt'};
par = [];
for i=1:length(mdl.parameters)
eval(strcat(mdl.parameters{i}, '=sym(''', mdl.parameters{i}, "');"));
eval(sprintf(['par = [par;' mdl.parameters{i} '];']));
end
%% Calculate stuff
matlabFunction(MM,'file',[modelName '_mass'],'vars',{par},'outputs',{'M'});
Code using the generated file:
getparams
load('m3d_1')
par = [];
for i=1:length(mdl.parameters)
eval(sprintf(['par = [par;params.' mdl.parameters{i} '];']));
end
See how, as long as I specify the correct value to for example params.mp, it always gets assigned to the input corresponding to the symbolic variable mp in the par vector. I do not want to lose that and have to keep track of the order and so on, nor do I want to call my functions with all the parameters one by one.
Actually, I see nothing wrong in your approach even if the "public opinion" affirms that it's better to avoid using the eval function. An alternative would be using the assignin function as follows:
% use 'caller' instead of 'base' if this code runs within a function
for i = 1:numel(mdl.parameters)
var_name = mdl.parameters{i};
assignin('base',var_name,sym(var_name));
end
In the second case (the one concerning the par variable) I would instead use the getfield function:
par_len = numel(mdl.parameters);
par = cell(par_len,1);
for i = 1:par_len
par{i} = getfield(params,mdl.parameters{i});
end
or, alternatively, this approach:
par_len = numel(mdl.parameters);
par = cell(par_len,1);
for i = 1:par_len
par{i} = params.(mdl.parameters{i});
end
When I was studying for my undergraduate degree in EE, MATLAB required each function to be defined in its own file, even if it was a one-liner.
I'm studying for a graduate degree now, and I have to write a project in MATLAB. Is this still a requirement for newer versions of MATLAB?
If it is possible to put more than one function in a file, are there any restrictions to this? For instance, can all the functions in the file be accessed from outside the file, or only the function that has the same name as the file?
Note: I am using MATLAB release R2007b.
The first function in an m-file (i.e. the main function), is invoked when that m-file is called. It is not required that the main function have the same name as the m-file, but for clarity it should. When the function and file name differ, the file name must be used to call the main function.
All subsequent functions in the m-file, called local functions (or "subfunctions" in the older terminology), can only be called by the main function and other local functions in that m-file. Functions in other m-files can not call them. Starting in R2016b, you can add local functions to scripts as well, although the scoping behavior is still the same (i.e. they can only be called from within the script).
In addition, you can also declare functions within other functions. These are called nested functions, and these can only be called from within the function they are nested. They can also have access to variables in functions in which they are nested, which makes them quite useful albeit slightly tricky to work with.
More food for thought...
There are some ways around the normal function scoping behavior outlined above, such as passing function handles as output arguments as mentioned in the answers from SCFrench and Jonas (which, starting in R2013b, is facilitated by the localfunctions function). However, I wouldn't suggest making it a habit of resorting to such tricks, as there are likely much better options for organizing your functions and files.
For example, let's say you have a main function A in an m-file A.m, along with local functions D, E, and F. Now let's say you have two other related functions B and C in m-files B.m and C.m, respectively, that you also want to be able to call D, E, and F. Here are some options you have:
Put D, E, and F each in their own separate m-files, allowing any other function to call them. The downside is that the scope of these functions is large and isn't restricted to just A, B, and C, but the upside is that this is quite simple.
Create a defineMyFunctions m-file (like in Jonas' example) with D, E, and F as local functions and a main function that simply returns function handles to them. This allows you to keep D, E, and F in the same file, but it doesn't do anything regarding the scope of these functions since any function that can call defineMyFunctions can invoke them. You also then have to worry about passing the function handles around as arguments to make sure you have them where you need them.
Copy D, E and F into B.m and C.m as local functions. This limits the scope of their usage to just A, B, and C, but makes updating and maintenance of your code a nightmare because you have three copies of the same code in different places.
Use private functions! If you have A, B, and C in the same directory, you can create a subdirectory called private and place D, E, and F in there, each as a separate m-file. This limits their scope so they can only be called by functions in the directory immediately above (i.e. A, B, and C) and keeps them together in the same place (but still different m-files):
myDirectory/
A.m
B.m
C.m
private/
D.m
E.m
F.m
All this goes somewhat outside the scope of your question, and is probably more detail than you need, but I thought it might be good to touch upon the more general concern of organizing all of your m-files. ;)
Generally, the answer to your question is no, you cannot define more than one externally visible function per file. You can return function handles to local functions, though, and a convenient way to do so is to make them fields of a struct. Here is an example:
function funs = makefuns
funs.fun1=#fun1;
funs.fun2=#fun2;
end
function y=fun1(x)
y=x;
end
function z=fun2
z=1;
end
And here is how it could be used:
>> myfuns = makefuns;
>> myfuns.fun1(5)
ans =
5
>> myfuns.fun2()
ans =
1
The only way to have multiple, separately accessible functions in a single file is to define STATIC METHODS using object-oriented programming. You'd access the function as myClass.static1(), myClass.static2() etc.
OOP functionality is only officially supported since R2008a, so unless you want to use the old, undocumented OOP syntax, the answer for you is no, as explained by #gnovice.
EDIT
One more way to define multiple functions inside a file that are accessible from the outside is to create a function that returns multiple function handles. In other words, you'd call your defining function as [fun1,fun2,fun3]=defineMyFunctions, after which you could use out1=fun1(inputs) etc.
I really like SCFrench's answer - I would like to point out that it can easily be modified to import the functions directly to the workspace using the assignin function. (Doing it like this reminds me a lot of Python's "import x from y" way of doing things)
function message = makefuns
assignin('base','fun1',#fun1);
assignin('base','fun2',#fun2);
message='Done importing functions to workspace';
end
function y=fun1(x)
y=x;
end
function z=fun2
z=1;
end
And then used thusly:
>> makefuns
ans =
Done importing functions to workspace
>> fun1(123)
ans =
123
>> fun2()
ans =
1
Along the same lines as SCFrench's answer, but with a more C# style spin..
I would (and often do) make a class containing multiple static methods. For example:
classdef Statistics
methods(Static)
function val = MyMean(data)
val = mean(data);
end
function val = MyStd(data)
val = std(data);
end
end
end
As the methods are static you don't need to instansiate the class. You call the functions as follows:
data = 1:10;
mean = Statistics.MyMean(data);
std = Statistics.MyStd(data);
I define multiple functions in one .m file with Octave and then use the command from within the .m file where I need to make use of the functions from that file:
source("mycode.m");
Not sure if this is available with Matlab.
octave:8> help source
'source' is a built-in function
-- Built-in Function: source (FILE)
Parse and execute the contents of FILE. This is equivalent to
executing commands from a script file, but without requiring the
file to be named `FILE.m'.
You could also group functions in one main file together with the main function looking like this:
function [varargout] = main( subfun, varargin )
[varargout{1:nargout}] = feval( subfun, varargin{:} );
% paste your subfunctions below ....
function str=subfun1
str='hello'
Then calling subfun1 would look like this:
str=main('subfun1')
As of R2017b, this is not officially possible. The relevant documentation states that:
Program files can contain multiple functions. If the file contains only function definitions, the first function is the main function, and is the function that MATLAB associates with the file name. Functions that follow the main function or script code are called local functions. Local functions are only available within the file.
However, workarounds suggested in other answers can achieve something similar.
I have try with the SCFRench and with the Ru Hasha on octave.
And finally it works: but I have done some modification
function message = makefuns
assignin('base','fun1', #fun1); % Ru Hasha
assignin('base', 'fun2', #fun2); % Ru Hasha
message.fun1=#fun1; % SCFrench
message.fun2=#fun2; % SCFrench
end
function y=fun1(x)
y=x;
end
function z=fun2
z=1;
end
Can be called in other 'm' file:
printf("%d\n", makefuns.fun1(123));
printf("%d\n", makefuns.fun2());
update:
I added an answer because neither the +72 nor the +20 worked in octave for me.
The one I wrote works perfectly (and I tested it last Friday when I later wrote the post).
I am writing a signal processing program using matlab. I know there are two types of float-pointing variables, single and double. Considering the memory usage, I want my code to work with only single type variable when the system's memory is not large, while it can also be adapted to work with double type variables when necessary, without significant modification (simple and light modification before running is OK, i.e., I don't need runtime-check technique). I know this can be done by macro in C and by template in C++. I don't find practical techniques which can do this in matlab. Do you have any experience with this?
I have a simple idea that I define a global string containing "single" or "double", then I pass this string to any memory allocation method called in my code to indicate what type I need. I think this can work, I just want to know which technique you guys use and is widely accepted.
I cannot see how a template would help here. The type of c++ templates are still determined in compile time (std::vector vec ...). Also note that Matlab defines all variables as double by default unless something else is stated. You basically want runtime checks for your code. I can think of one solution as using a function with a persistent variable. The variable is set once per run. When you generate variables you would then have to generate all variables you want to have as float through this function. This will slow down assignment though, since you have to call a function to assign variables.
This example is somehow an implementation of the singleton pattern (but not exactly). The persistent variable type is set at the first use and cannot change later in the program (assuming that you do not do anything stupid as clearing the variable explicitly). I would recommend to go for hardcoding single in case performance is an issue, instead of having runtime checks or assignment functions or classes or what you can come up with.
function c = assignFloat(a,b)
persistent type;
if (isempty(type) & nargin==2)
type = b;
elseif (isempty(type))
type = 'single';
% elseif(nargin==2), error('Do not set twice!') % Optional code, imo unnecessary.
end
if (strcmp(type,'single'))
c = single(a);
return;
end
c = double(a);
end
When I was studying for my undergraduate degree in EE, MATLAB required each function to be defined in its own file, even if it was a one-liner.
I'm studying for a graduate degree now, and I have to write a project in MATLAB. Is this still a requirement for newer versions of MATLAB?
If it is possible to put more than one function in a file, are there any restrictions to this? For instance, can all the functions in the file be accessed from outside the file, or only the function that has the same name as the file?
Note: I am using MATLAB release R2007b.
The first function in an m-file (i.e. the main function), is invoked when that m-file is called. It is not required that the main function have the same name as the m-file, but for clarity it should. When the function and file name differ, the file name must be used to call the main function.
All subsequent functions in the m-file, called local functions (or "subfunctions" in the older terminology), can only be called by the main function and other local functions in that m-file. Functions in other m-files can not call them. Starting in R2016b, you can add local functions to scripts as well, although the scoping behavior is still the same (i.e. they can only be called from within the script).
In addition, you can also declare functions within other functions. These are called nested functions, and these can only be called from within the function they are nested. They can also have access to variables in functions in which they are nested, which makes them quite useful albeit slightly tricky to work with.
More food for thought...
There are some ways around the normal function scoping behavior outlined above, such as passing function handles as output arguments as mentioned in the answers from SCFrench and Jonas (which, starting in R2013b, is facilitated by the localfunctions function). However, I wouldn't suggest making it a habit of resorting to such tricks, as there are likely much better options for organizing your functions and files.
For example, let's say you have a main function A in an m-file A.m, along with local functions D, E, and F. Now let's say you have two other related functions B and C in m-files B.m and C.m, respectively, that you also want to be able to call D, E, and F. Here are some options you have:
Put D, E, and F each in their own separate m-files, allowing any other function to call them. The downside is that the scope of these functions is large and isn't restricted to just A, B, and C, but the upside is that this is quite simple.
Create a defineMyFunctions m-file (like in Jonas' example) with D, E, and F as local functions and a main function that simply returns function handles to them. This allows you to keep D, E, and F in the same file, but it doesn't do anything regarding the scope of these functions since any function that can call defineMyFunctions can invoke them. You also then have to worry about passing the function handles around as arguments to make sure you have them where you need them.
Copy D, E and F into B.m and C.m as local functions. This limits the scope of their usage to just A, B, and C, but makes updating and maintenance of your code a nightmare because you have three copies of the same code in different places.
Use private functions! If you have A, B, and C in the same directory, you can create a subdirectory called private and place D, E, and F in there, each as a separate m-file. This limits their scope so they can only be called by functions in the directory immediately above (i.e. A, B, and C) and keeps them together in the same place (but still different m-files):
myDirectory/
A.m
B.m
C.m
private/
D.m
E.m
F.m
All this goes somewhat outside the scope of your question, and is probably more detail than you need, but I thought it might be good to touch upon the more general concern of organizing all of your m-files. ;)
Generally, the answer to your question is no, you cannot define more than one externally visible function per file. You can return function handles to local functions, though, and a convenient way to do so is to make them fields of a struct. Here is an example:
function funs = makefuns
funs.fun1=#fun1;
funs.fun2=#fun2;
end
function y=fun1(x)
y=x;
end
function z=fun2
z=1;
end
And here is how it could be used:
>> myfuns = makefuns;
>> myfuns.fun1(5)
ans =
5
>> myfuns.fun2()
ans =
1
The only way to have multiple, separately accessible functions in a single file is to define STATIC METHODS using object-oriented programming. You'd access the function as myClass.static1(), myClass.static2() etc.
OOP functionality is only officially supported since R2008a, so unless you want to use the old, undocumented OOP syntax, the answer for you is no, as explained by #gnovice.
EDIT
One more way to define multiple functions inside a file that are accessible from the outside is to create a function that returns multiple function handles. In other words, you'd call your defining function as [fun1,fun2,fun3]=defineMyFunctions, after which you could use out1=fun1(inputs) etc.
I really like SCFrench's answer - I would like to point out that it can easily be modified to import the functions directly to the workspace using the assignin function. (Doing it like this reminds me a lot of Python's "import x from y" way of doing things)
function message = makefuns
assignin('base','fun1',#fun1);
assignin('base','fun2',#fun2);
message='Done importing functions to workspace';
end
function y=fun1(x)
y=x;
end
function z=fun2
z=1;
end
And then used thusly:
>> makefuns
ans =
Done importing functions to workspace
>> fun1(123)
ans =
123
>> fun2()
ans =
1
Along the same lines as SCFrench's answer, but with a more C# style spin..
I would (and often do) make a class containing multiple static methods. For example:
classdef Statistics
methods(Static)
function val = MyMean(data)
val = mean(data);
end
function val = MyStd(data)
val = std(data);
end
end
end
As the methods are static you don't need to instansiate the class. You call the functions as follows:
data = 1:10;
mean = Statistics.MyMean(data);
std = Statistics.MyStd(data);
I define multiple functions in one .m file with Octave and then use the command from within the .m file where I need to make use of the functions from that file:
source("mycode.m");
Not sure if this is available with Matlab.
octave:8> help source
'source' is a built-in function
-- Built-in Function: source (FILE)
Parse and execute the contents of FILE. This is equivalent to
executing commands from a script file, but without requiring the
file to be named `FILE.m'.
You could also group functions in one main file together with the main function looking like this:
function [varargout] = main( subfun, varargin )
[varargout{1:nargout}] = feval( subfun, varargin{:} );
% paste your subfunctions below ....
function str=subfun1
str='hello'
Then calling subfun1 would look like this:
str=main('subfun1')
As of R2017b, this is not officially possible. The relevant documentation states that:
Program files can contain multiple functions. If the file contains only function definitions, the first function is the main function, and is the function that MATLAB associates with the file name. Functions that follow the main function or script code are called local functions. Local functions are only available within the file.
However, workarounds suggested in other answers can achieve something similar.
I have try with the SCFRench and with the Ru Hasha on octave.
And finally it works: but I have done some modification
function message = makefuns
assignin('base','fun1', #fun1); % Ru Hasha
assignin('base', 'fun2', #fun2); % Ru Hasha
message.fun1=#fun1; % SCFrench
message.fun2=#fun2; % SCFrench
end
function y=fun1(x)
y=x;
end
function z=fun2
z=1;
end
Can be called in other 'm' file:
printf("%d\n", makefuns.fun1(123));
printf("%d\n", makefuns.fun2());
update:
I added an answer because neither the +72 nor the +20 worked in octave for me.
The one I wrote works perfectly (and I tested it last Friday when I later wrote the post).
One of the fields in my structure is a function handle:
strct.handl=#(arg1,arg2)handl(arg1,arg2,par1,par2)
Now, arg1 and arg2 are defined every time I use the handle, but par1 and par2 are stored when I define the handle. Thus, (correct me if I'm wrong), handle functions like a pointer to par1 and par2.
In either case, my question is how I can see how much space in my memory handle is taking up because it also 'points' to par1 & par2. However, if I use whos('handl'), I will only get the size of the handle, not handle+par1+par2.
Thanks!
When you construct the anonymous function, you are creating a closure (the function captures any variables defined in its outer scope).
You can use the functions method to get the captured workspace of a function handle:
>> a = 1;
>> f = #(x) x+a;
>> S = functions(f)
S =
function: '#(x)x+a'
type: 'anonymous'
file: ''
workspace: {[1x1 struct]}
>> S.workspace{1}
ans =
a: 1
I just want to address the memory usage issue that #DankMasterDan pointed out; MATLAB uses a copy-on-write strategy, so if variables in the enclosing workspace are not changed after being captured, you will not incur additional memory usage.
I wanted to add that that when you use anonymous functions in matlab, not only does it save the input arguments in its workspace, it also saves the ENTIRE workspace it was created in into its workspace.
As, in my case, this led to a huge ballooning of memory usage. Thus, I will revent back to normal handles..!