I run a program, which is a function - here I'll call it 'myfxn' - that outputs several different variables. But when I try to access the data I get
??? Undefined function or variable 'myfxn'.
How do I access the data? Thanks for your help.
Your question is a bit confusing - you claim you run the function, but then you also say that Matlab throws an error indicating it can't run the function.
Here's two things to test
Is myfxn on the Matlab path? Run the command which myfxn. If that does not find the function, change directory (using cd or the directory browser on the Matlab Desktop) to where myfxn is located.
Does the function actually generate output? If it's a function, the first line should look something like this: function [out1,out2] = myfxn(in1,in2), where in1 and in2 are two input arguments, and out1 and out2 are output arguments. Then, you could call myfxn like this: [a,b] = myfxn(2,'something');, and it will use the two inputs to generate the two outputs, which are assigned to a, and b, respectively.
Related
I am writing a script to access a function that has been written in another script.
When I run the second script the error is that the function is undefined.
I have been working backwards and am currently trying to get the function to work in the command window.
The function file has appeared in the current folder window. When it is highlighted all functions and parameters are displayed in the window below (displays the file name on top then the file contents).
I am still getting a function is undefined when I copy and paste the functions call from the script into the command window.
I tried rebuilding the functions individually in separate scripts, but I am still receiving an error message.
I have made sure the are in the same folder, and are spelled exactly the same, what am I doing wrong?
'''
%file name Lab_5_functions.m
function[vel] = velocity (g,m,co_d,t)
vel= ((g*m)/co_d)^(1/2)*tanh(((g*co_d)/m)^(1/2)*t);
end
function [dvel]= dvelocity (g,m,co_d,t)
dvel=(((.5*(g*m)/co_d)^(1/2)*tanh(((g*co_d)/m).^(1/2)*t_sec))-(((g*t)/(2*m))*(sech(((g*co_d)./m).^(1/2)*t))));
end
'''
v=velocity(1,2,3,4)
%error message below:
Undefined function or variable 'velocity'.
'''
Thanks
-MK
Matlab is searching for functions using filenames. So you define a single public function myfunc in a file myfunc.m.
You can define additional functions in that file, but they will not be accessible outside that .m file.
MATLAB looks for filenames to find the functions and expects the first line of that file to be a function definition.
For example: myfunc.m
function output = myfunc(input)
If you do want many functions in one file (like a module/library), I have used a work-around before: write all your functions in the file, then include an if-else block to call the correct function. Multiple arguments can be parsed with some simple checks (see nargin function). It is a less elegant solution; I only use it if I have many simple functions and it would be plain annoying to have heaps of .m files.
Here is a simple example:
Call the file: myfunc.m
function output = myfunc(fn, arg1, arg2, ...)
function out = func1(arg1, arg2, ...)
out = 0
if strcmp(fn, 'func1')
if nargin == 2
output = func1(arg1)
end
elseif strcmp(fn, 'func2')
...
end
I'm trying to get started with Matlab / Octave and having a difficult time figuring how to organize a program into functions. Currently I'm trying to write a simple program that adds two numbers together and displays the result, with the adding being done by a function. I would have figured this would have worked:
% test.m
close all;
clear all;
num1 = 2;
num2 = 2;
result = myAdd(num1, num2);
disp(result); % this should display 4 ??
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function retval = myAdd(var1, var2)
retval = var1 + var2;
end
Running the above with Octave 4.0.0, I get the following errors:
error: 'myAdd' undefined near line 7 column 10
error: called from
test at line 7 column 8
I have tried also putting the function first and the test part second, and also putting the function in a separate file and having a main.m file in the same directory call the myAdd function, all result in errors.
So here are my questions:
-Does Matlab / Octave have a main equivalent ??
-How does the interpreter know where to start? Does it automatically go to the first line in the program, or is there a certain function name you can use to make it start with that function as function main() is in C/C++ ??
-In a Python program of significant size, my usual practice is to organize things as follows:
# some_python_program.py
import abc
import xyz
###################################################################################################
def main():
# stuff to get program started here
# end main
###################################################################################################
def function1():
# specific function here
# end function
###################################################################################################
def function2():
# specific function here
# end function
###################################################################################################
if __name__ == "__main__":
main()
Is there a way to do the equivalent in Matlab/Octave ??
If somebody could provide some direction as to a main equivalent and/or how to organize functions in Matlab/Octave please advise, thanks.
Matlab/Octave can be a bit confusing in this way if you're coming from a language like python. In order to define a function (without using anonymous functions), you need to create a separate file with the name of that function, which can then be called using the command line.
For example, you would like to create a function called myadd. You should create a file named myadd.m whose contents will be:
function out = myadd(a,b)
out = a+b;
end
Then, as long as your file is on your path (save it to your MATLAB folder or put it in your current working directory), you can call it from the Command Window as follows:
>> myadd(5,6)
ans =
11
Only one function will be made publicly available per file (the one whose name matches the file name). However, you can still define multiple functions per file if you plan to use only that function. For example, if you have a file named foo.m, you can do the following:
function out = foo(a,b)
out = fun(a,b);
end
function out = fun(a,b)
out = a * b;
end
This will allow you to call foo(5,6) from the Command Window, but fun(5,6) will result in an error: Undefined function or variable 'fun'.
Read more about local functions and nested functions.
Hope this is helpful!
I'm experiencing a puzzling error in Matlab R2012b. It seems that variable names that are also data types exhibit strange behavior. Please see this small example:
function [] = test1()
dataset = 1;
if dataset ~= 0
disp hello
end
end
A call to test1() produces output hello, as expected.
Now, rather than set the value of dataset in my function, I run a script instead.
function [] = test2()
myscript;
if dataset ~= 0
disp hello
end
end
where myscript.m has one line:
dataset=1;
Now, when I call test2() I get this error:
Undefined function 'ne' for input arguments of type 'dataset'.
Error in test2 (line 4)
if dataset ~= 0
(Forgive the variable named dataset - I know that it is also the name of a data type, and it came in the code I was running.) So it seems as if in test2, Matlab creates an empty dataset object rather than using the variable named dataset. Furthermore, this behavior only appears when I set the value in a script rather than in the function body. Even more weird, is that I can do:
>> dbstop in test2 at 4 % line of if statement
>> test2()
K>> dataset
dataset =
1.00
K>> dataset ~= 0
ans =
1
K>> if dataset ~= 0, disp hello; end
hello
K>> dbcont
and I get the same error! The error is not displayed in debugging mode but it is in normal execution.
Can anyone reproduce this? What is going on here?
The MATLAB online help has some pages dealing with this issue; Variables Names and Loading Variables within a Function seem to be the most relevant.
There is no explicit page that discusses how MATLAB resolves names at compilation time, but there is one little tidbit at the bottom of the Variables Names page: "In some cases, load or eval add variables that have the same names as functions. Unless these variables are in the function workspace before the call to load or eval, the MATLAB parser interprets the variable names as function names."
In other words, if the parser finds an explicit assignment to a variable whose name is the same as another existent object, the local definition takes precedence.
In your test2(), there is no explicit assignment to a variable dataset; therefore, when the file is compiled, the parser interprets dataset to be a class constructor (since the parser will not run or inline myscript into the function).
Then at run-time, even though a variable named dataset has been poofed1 into the function's workspace, the interpreted code that is running still has the dataset symbol in the if-statement associated with the class constructor.
If you need to, you can still use the dataset variable name and load from an external file, but it should be done with an explicit assignment via a function call. For example:
dataset = initialize();
Now the parser will notice that dataset is some arbitrary output of the function initialize and all will be well. In fact, you can have even have initialize return a dataset constructor to the dataset variable if you wanted.
1 When variables are defined without explicit assignment, MATLAB people (at least on some of their blogs I've read) called this 'poofing'. Using load without any output arguments, using eval, and simply running scripts (not functions) can all poof variables into the workspace. This can work fine as long as the variable names do not conflict with other in-use symbols at compile time.
I have a function
function [ obsTime, obsWDIR, obsWSPD, obsSWH, obsMWD ] = readObsC(obsFile, endTime)
that when I run it, it gives an output of a huge array ans, which is the same array as obsTime. But obsTime, obsWDIR, obsWSPD, etc. don't display. Not a single line of code is supposed to display ans.
When I'm in debugging mode, I run the code and stop it at the very last line, and it doesn't give an output ans. Only when I hit 'step' twice and the function ends, does the ans output appear.
Everything in the function has semicolons.
Why does ans appear? Where are my other outputs?
In your function definition, you name the formal input and output arguments. That determines the name which these arguments will use within the function.
The function has its own environment, and variable names inside the function are completely independent of variable names outside the function, unless you use global or evalin('caller').
You have to provide actual input and output arguments at the time of the call, which determines how the code outside the function refers to those same arguments. There is no automatic passing of arguments simply because the names match! The only automatic thing is that if you don't specify the actual output arguments, the first actual output argument will be ans and the rest are discarded.
You could have figured this out if you simply read the MATLAB documentation for ans:
The MATLAB® software creates the ans variable automatically when you specify no output argument.
The function declaration specifies the return values, but when you call it, you don't specify anywhere for the output to go. When you call something on the command line, the output is always defaulted to ans unless you assign a variable to the output of the function when you call it.
I defined a simple function called myfunc as:
function [one,two,three,four] = myfunc(value1,value2)
Ex, using workspace variables (denoted ws_) to capture function output:
>> [ws_one,ws_two,ws_three,ws_four] = myfunc(1,2)
prints:
ws_one =
1
ws_two =
2
ws_three =
1
ws_four =
2
I'm quite new to Matlab. I've defined a function inside a .m file, I want to use that function in that .m file inside another .m file, and I want to run the contents of that last .m file from the command window.
How should I go about accomplishing this?
EDIT- for clarification, I have one function a inside a.m, and a script inside b.m that uses the function a inside a.m. I would like to run this script inside b.m from the command window, but am not sure how to do so. (as a side note, I can totally convert the script in b.m into a function if need be)
EDIT- right now I just need to know how to import/load a matlab file and that is it!!!
If I understand your situation correctly, you have something like this:
A file (`A.m'):
function results = A(parameters)
% some code
A file (`B.m'):
function results = B(parameters)
% some code
You want to use function A inside B, you can just call that function from inside function B:
function results = B(parameters)
% some code
otherResults = A(otherParameters)
If your situation is something like what nimrodm described, your A.m file is something like:
function results = A(paramters)
% some code
function results = C(parameters)
% code of function C
end
end
function results = D(parameters)
% code of function D
end
There is no way of directly accessing C and D from outside A. If you need to use subfunction D outside of A, just make a file D.m containing
function results = D(parameters)
% code of function D
end
And preferably, removed the same code from function A.
For a nested function C, the same can be done in some (but not all) cases, as nested functions also have access to the variables of function A. In recent versions of MATLAB (I guess R2010b or R2011a), the editor highlights variables that are shared between a function and nested functions in teal. If you don't make use of the variables of function A inside of function C, just do the same as for function D. If you do, pass these variables as parameters and/or return values and adjust the rest of your code to reflect this. Test your code and afterwards, do the same as for D.
Most likely, you will not have case C, as this is an advanced feature in MATLAB.
There is however another case, if you are not using MATLAB functions, but MATLAB scripts in different files. You can call a script (both from command line and another function or script, just by its (file) name.
contents of file E.m:
% code for script E
contents of file F.m:
% some code
E;
Using that code, you execute all commands in E from inside script F. Beware that E and F will share all their variables, so if you begin your scripts by something like clear all; close all; clc;, you cannot pass any variables from F into E (and you will lose all results from F calculated before calling E.
In most cases it is better to use functions instead of scripts, so that's also the way to solve such a situation: make everything into functions with decent parameters and return values.
edit:
After you 'changed' your question, it's quite easy.
Let's consider you have the function, I will use different names, as that is more intuitive to understand. You have the function ackermann inside the file ackermann.m which you want to call from the script bigScript.m.
The file ackermann.m contains the Ackermann-Péter function (as an example):
function result = ackermann(m,n)
if m == 0
result = n + 1;
elseif m > 0
if n == 0
result = ackermann(m-1,1);
elseif n > 0
result = ackermann(m-1,ackermann(m,n-1));
else
error('n has to be positive');
end
else
error('m has to be positive');
end
end
From inside your big script, you can call the function ackermann as follows (if you want m = 1 and n = 1):
A = ackermann(1,1)
It's that simple, no need to load anything. But you need to remember to have the function 'available in your path', the easiest way to do this, is just keep the script and function files in the same directory.
Anyhow, I sense you are a starting MATLAB user: if you don't know what a function does, just type help functionname (substituting functionname of course) into the command window. You will notice that the function load is there to load data files, not for m-files (as the m-files in your path are used automatically).
In principle, MATLAB advocates the use of one function per .m file. You can call such a function from another .m file and from the MATLAB command line.
You can define multiple functions in one .m file, but only the first (or 'outermost') function can be accessed from other .m files or the command line. The other functions are treated as 'helper' functions that may be called only inside this particular .m file.
For anyone else searching for this question, as I did, just type:
addpath('[Path name of mat file]');
This will tell Matlab how to find the function. To verify, just type:
which [function name]
If successful, it should list the path name that you just added.