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
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 wrote a function A in matlab that takes inputs and reshapes them. Next of it calls another function in sub directories B with these reshaped arguments. The function B should be executed a code on directory that have passed to it. The function B works with string of directory explicitly passed to it. But when i generate string of same directory and passes to it. it does not execute.
here is the error:
Undefined function 'B' for input arguments of type 'char'.
the code of function A
function [ Data ] = A( DataSet,fileName )
root = getenv('Project');
addpath /Subdirectory
Data = B(strcat(root,'\Features\',DataSet,'\',fileName));
end
You should probably try with
addpath ./Subdirectory.
Besides, it seems that you are working on Windows (because of the backslashes '\Features',etc), so maybe you should try addpath .\Subdirectory
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 need to write a function whose input argument should be file name, and the function will perform certain operation on the opened file. Here is the sample function I wrote,
function readFile = loadOneColumnFile(fileName)
fid1 = fopen(fileName);
readFile = 0;
fclose(fid1);
But when I invoke this function in the command console as follows,
>> testValue = loadOneColumnCSV('/usr1/test.csv');
The Matlab returns the following error message
??? Undefined function or method 'loadOneColumnFile' for input arguments of type 'char'.
Looks like that the definition of function is not correct. How to fix it? Thanks.
MATLAB treats a string as an array of characters (like C++, except the strings are not null-terminated in MATLAB).
Despite the error message, I don't think there is any problem with the string passing. The problem is MATLAB cannot find your function. So:
The file containing the function must have same name as the function (in your case save the function in a file named loadOneColumnFile.m)
The loadOneColumnFile.m must be placed in the working (current) directory so MATLAB could find it.
The name of the function is not consistent in your question. Make sure you have used only one of the loadOneColumnFile or loadOneColumnCSV for naming the function and filename.
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.