I have a script with a loop going over several different value combinations. This script calls the main with the value combinations, which then calls a parfor which accesses the different values. In the following is a dummy simplification of my code. If needed, I will supply the full code.
Loop:
a = [0.3, 0.4, 0.5, 0.6, 0.7, 0.8];
b = [5,10,15,20,25,30];
c = [0,1];
% Iterate over all possible combinations
for p = 1:length(a)
for s = 1:length(b)
for e = 1:length(c)
main(p,s,e); clear all;
end
end
end
Main:
function main (p,s,e)
parfor k = 1:51
if(e)
display('Foobar');
end
end
end
So I basically want to decide in the parfor loop what to do (e.g. how to create intervals etc.) with the help of the input parameters. I do not want to edit this parameters, just read and use them.
Now I get the following error:
An UndefinedFunction error was thrown on the workers for 'e'. This
might be because the file containing 'e' is not accessible on the
workers. Use addAttachedFiles(pool, files) to specify the required
files to be attached. See the documentation for
'parallel.Pool/addAttachedFiles' for more details.
I don't get why this does not work. Just defining e again, like
e2 = e
does not help either.
Greetings
Edit:
What actually seems to work is when I pass not the variables of the for loop directly to the main but actually use the arrays like intended.
E.g.:
main(a(p),b(s),c(e))
I found the solution.
I tried to pass the variables assigned to go through the for loops to the main function. This is not possible.
What I actually wanted (and did) now instead is passing a value from the arrays defined before to the main function.
a = [0.3, 0.4, 0.5, 0.6, 0.7, 0.8];
b = [5,10,15,20,25,30];
c = [0,1];
% Iterate over all possible combinations
for p = 1:length(a)
for s = 1:length(b)
for e = 1:length(c)
main(a(p),b(s),c(e)); clear all;
end
end
end
Related
I've written the following piece of subcode (with parameters commented) for an Euler policy iteration algorithm. When I try to run the body of the function (everything below global) for say, a1 = 1, it works, and returns a scalar. However, when I call the function as euler_diff_test(1), I get an error. (Pasted below)
function diff = euler_diff_test(a1)
%the following comments are example parameters. They are in the global line originally.
% r = 0.2, a = 0.5, y = 1.1, a_grid = linspace(0.5,7,100)
%policy_guess = zeros(2,N);
%policy_guess(1,:) = 0.3*a_grid;
%policy_guess(2,:) = 0.3*a_grid;
% M = zeros(2,2); %M for markov transition kernel
% M(1,1) = p;
% M(2,2) = p;
% M(2,1) = 1-p;
% M(1,2) = 1-p;
% j = 1
global r a y a_grid policy_guess M j;
c = (1+r)*a + y - a1; %consumption formula
if c<=1e-02 %don't care about consumption being negative
diff = 888888888888888888888;
else
policy_func = interp1(a_grid', policy_guess', a1, 'linear');
diff = 1/c - beta*(1+r)*(1 ./ policy_func)*M(j,:)';
end
end
Error Reads:
Any help is much appreciated!
The problem is that you dont understand globals nor how they work!
You seem to be doing something like:
N=100; p=0.1;
r = 0.2, a = 0.5, y = 1.1, a_grid = linspace(0.5,7,100)
policy_guess = zeros(2,N);
policy_guess(1,:) = 0.3*a_grid;
policy_guess(2,:) = 0.3*a_grid;
M = zeros(2,2); %M for markov transition kernel
M(1,1) = p;
M(2,2) = p;
M(2,1) = 1-p;
M(1,2) = 1-p;
euler_diff_test(1)
And this is causing the error you show. Of course it is!
First, you need to learn what a global is and what worskpaces are. Each fucntion has its own worskpace or "scope". That means that only variables defined within the workspace are visible by the function itself.
A global variable is one that exist for all workspaces, and everyone can modify it. You seem to want all those variables defined outside the function, inside your function. But realise! when the variables are defined, they are not global. The function starts, and in its first line, it does only know about the existence of a1. Then, later, you define a bunch of variables as global, that the function did not know about. So what does the function do? just create them empty, for you.
If you want your the variables that you create in the main script scope to be global, you need to declare them as global then, not inside the function. So cut your line global ... from the fucntion, and put it on top of the script where you declare all your variables, i.e. on top of
% here!
N=100; p=0.1;
...
in my example.
Now, the important stuff: Global variables are bad. When you have globals, you don't know who modifies, and its super easy to lost track of what is happening to them, because every function that uses a variable a will modify the global a, so its a pain to debug. Almost no one uses globals because of this. The best way is to pass them to the function as input, i.e. define your function as:
function diff = euler_diff_test(a1,r, a, y, a_grid, policy_guess, M, j)
Can we configure MATLAB let variable have minium local scope?
I want matlab something similiar like C below.
% after some configure ...
for i=1:1:100
a=i*i
end
% here we can not using 'a' any more for it have local scope in for loop.
Why I want it becase the scope in whole script sometimes leds to bug hard to find.
For example:
% get accumulate of b via 100 times of x_0
b=0;
for i=1:1:100
x0=100
b=b+x0
end
% get accumulate of a via 100 times of x_0
a=0
for i=1:1:100
x_0=200
a=a+x0 %mistype x_0 to x0, and hard to find
end
Thanks advance.
I don't think there is any way to force a local scope in a script/loop. However, you can create a function, in a separate file or in the same file. Each function will have it's own local scope. So for your example you can create a file myScript.m with the following:
% get accumulate of b via 100 times of x_0
accum_b(100)
% get accumulate of a via 100 times of x_0
accum_a(200)
function a = accum_a(x0)
a = 0;
for k = 1:100
a = a + x0;
end
end
function b = accum_b(x0)
b = 0;
for k = 1:100
b = b + x0;
end
end
In this particular example, you can of course call the accum_a function twice, with different x0 inputs. But each function you define in a file will have it's own local scope, and will thus result in an error when mistyping x_0/x0.
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.
In a matlab script, is it possible to define a variable after the function is called?
(i.e. the script finds the function with the undefined variable, looks for the variable initialization and executes the function afterwards)
I need this because I have a large number of variables and functions and I don't want to order them in a sequential way but in the way that is appropriate for my problem.
E.g.
mean(x);
x = [1, 2, 3];
Thanks
Disclaimer: I think what you want to do is a really bad practice. If you find yourself in the need to do this, your code screams refactoring.
Yes, it is possible. There are two ways.
Using the try-catch statement:
try
x_mean = mean(x)
catch exception
if isequal(exception.identifier, 'MATLAB:UndefinedFunction')
x = [1,2,3];
x_mean = mean(x);
else
rethrow(exception);
end
end
The explanation: if the mean(x) fails, the code will enter in the catch branch. Then it verifies that the error is happening because a missing variable and if that's the case, the variable x is defined and the function re-run. There is a caveat: Matlab uses the same identifier for missing variable and for missing function.
Using the exist function:
if exist('x') == 1 %// the function have several return values
x_mean = mean(x);
else
x = [1, 2, 3];
x_mean = mean(x);
end
The explanation: the exist function will verify if a variable with the name x exists in the workspace. If it does exist, it will return 1 and you can execute your function. If it does not exist, then you can declare it first and then run mean. See documentation here.
My two cents: once again, this is a horrible way to achieve things. By going this way you will end up with pure spaghetti code. It will be a nightmare to debug. It will be a nightmare to maintain. There is a 99% chance that there are better ways to do what you want. It is just a matter of investing time and think a little bit. Even if it is a personal project or a quick script to solve a homework/task, you will learn much more by doing it the right way.
If I understand you question correctly, then yes it can be done by some ugly hacks.
The following class can be used:
classdef AdvancedFunctionHandle
properties(GetAccess = 'private', SetAccess = 'private')
handle
variables
end
methods
function obj = AdvancedFunctionHandle(fct, varargin)
if ~isa(fct,'function_handle')
error('The function must be a function handle!');
end
argins = numel(varargin);
variables = cell(1,argins);
for i = 1:argins
if ~ischar(varargin{i})
error('The variables must be represented by a string variabel name!');
end
if (~isvarname(varargin{i}) )
error('The variables must be a string representing a legal variabel name!');
end
variables{i} = varargin{i};
end
obj.handle = fct;
obj.variables = variables;
end
function val = subsindex(obj)
val = obj.calculate();
end
function val = calculate(obj)
try
vars = cell(1,numel(obj.variables));
for i = 1:numel(obj.variables)
v = evalin('base',obj.variables{i});
if isa(v,'AdvancedFunctionHandle')
vars{i} = v.calculate();
else
vars{i} = v;
end
end
val = obj.handle(vars{:});
catch
val = obj;
end
end
function display(obj)
disp([func2str(obj.handle),'(',strjoin(obj.variables,','),')']);
end
end
end
I made a small test script for it too:
clear
m = AdvancedFunctionHandle(#mean,'x');
s = AdvancedFunctionHandle(#(n)sum(1:n),'m');
m.calculate
x = [1,2,3];
s.calculate
I hope this solves your problem.
Notice that since the class refers to the base workspace, it will not work when run from a function, or if the script it is run from is run from a function.
I don't understand what you are trying to achieve, but if you want to define things after they are used, I think they have to be functions.
Example file:
function myfun()
mean(getX)
function X = getX
X = [1 2 3]
So though it is technically possible to define variables after they are used, you would really not want to do that.
I am having trouble using struct arrays in Matlab's parfor loop. The following code has 2 problems I do not understand:
s=struct('a',{},'b',{});
if matlabpool('size')==0
matlabpool open local 2
end
for j = 1:2
parfor k=1:4
fprintf('[%d,%d]\n',k,j)
s(j,k).a = k;
s(j,k).b = j;
end
end
matlabpool close
It fails with an error Error using parallel_function (line 589)
Insufficient number of outputs from right hand side of equal sign to satisfy assignment.
On output, variable s is a vector, not an array (as it should be, even if the code breaks before finishing).
EDIT the problem is solved if I initialize the struct arrays to the correct size, by:
s=struct('a',cell(2,4),'b',cell(2,4));
However, I would still be happy to get insights about the problem (e.g is it rally a bug, as suggested by Oleg Komarov)
It was originally working fine for me but then I don't know what happens. In general you need to be careful with parfor loops and there are ample documentation on how to align everything. Two different words of advice.
First and more importantly, the parfor loop is on the outside loop:
function s = foo
s=struct('a',{},'b',{});
parfor j = 1:2
for k=1:4
fprintf('[%d,%d]\n',k,j)
s(j,k).a = k;
s(j,k).b = j;
end
end
Two, Matlab gets very picky about writing the main exit variable (i.e. the variable contained in the parfor loop which is indexed to the loop, in your case, s). You first want to create a dummy variable that holds all the innerloop information, and then writes to it once at the end of the loops. Example:
function s = khal
s=struct('a',{},'b',{});
parfor j = 1:2
dummy=struct('a',{},'b',{});
for k=1:4
fprintf('[%d,%d]\n',k,j)
dummy(k).a = k;
dummy(k).b = j;
end
s(j,:) = dummy;
end
You don't have a problem here, but it can get complicated in other instances