I wanted to code a function in octave, however I found some problems during doing so:
N=700;
T=900;
lambda=N/T;
x=randn(N,T);
s=std(x(:));
r=x*x'/T;
l=eig(r);
lambda_plus=(s^2)*(1+sqrt(lambda))^2;
lambda_minus=(s^2)*(1-sqrt(lambda))^2;
# Define a function - value of this function depenends
# on position of x
function kiki = avg (x)
if (x <= lambda_plus && x >= lambda_minus)
(1/(2*pi*lambda*x*s^(2)))*sqrt((lambda_plus-x)*(x-lambda_minus));
else
0
endif
endfunction
Then I wanted to run this function so I did run avg(2) but it didn't work.
Error I saw was:
error: 'lambda_plus' undefined near line 15, column 15
but it's not true! lambda_plus is defined before the definition of the function!
I read that this problem might be, because octave doesn't see our function and the solution is to:
(1) Save the file with name of the function - in my case avg.m
(2) Open a new file and in new file run your function
I did exactly what they were saying and in newly created file I ran avg(2) but unfortunately with exactly same result.
Related
I've a very newbie octave question.
Running this code in octave console is working fine:
function fibo = recfibo(n)
if ( n < 2 )
fibo = n;
else
fibo = recfibo(n-1) + recfibo(n-2);
endif
endfunction
disp(recfibo(5))
By inserting this code in an external file named for example file.m, and executing it through octave file.m an error occurs:
warning: function name 'recfibo' does not agree with function filename
'/Users/admin/Google Drive/file.m'
error: 'n' undefined near line 2 column 8 error: called from
octave at line 2 column 3
How should I resolve this particular problem?
Add 1; as the first line of the file:
1;
function fibo = recfibo(n)
if ( n < 2 )
fibo = n;
else
fibo = recfibo(n-1) + recfibo(n-2);
endif
endfunction
disp(recfibo(5))
Any M-file that starts with a function definition is a function M-file, not a script M-file. By adding a meaningless statement to the top, you turn it into a script.
In MATLAB (since fairly recently), a script M-file can define functions at the end of the script. There you'd put the disp line at the top of the file, and have the function block at the end, without any script lines after it. However, Octave requires functions to be defined before you use them, hence it has to come before the script line that uses the function. Octave allowed the definition of functions within a script file before MATLAB introduced that feature, hence their implementation is not compatible with that of MATLAB.
As stated in the answer provided by #CrisLuengo here you have created a function file instead of a script file and they are treated differently in Octave. Because it is a function file Octave executes it by calling the function it defines with no arguments and nargout = 0. So you will get an error that n is undefined.
Another problem is that the function name 'recfibo' does not agree with function filename 'file'. In such cases Octave internally changes the name of the function to the name of the function file so the name is changed to 'file'. Therefor Octave and the function itself will forget the original function name and unfortunately the function cannot call itself recursively!
I like the #CrisLuengo 's answer but I think the more idiomatic and preferable way is always using function files instead of script files, though the script file solution is the only solution that works in previous Octave versions (Octave 3.X).
You can change your code to:
function file
disp(recfibo(5))
endfunction
function fibo = recfibo(n)
if ( n < 2 )
fibo = n;
else
fibo = recfibo(n-1) + recfibo(n-2);
endif
endfunction
I've a very newbie octave question.
Running this code in octave console is working fine:
function fibo = recfibo(n)
if ( n < 2 )
fibo = n;
else
fibo = recfibo(n-1) + recfibo(n-2);
endif
endfunction
disp(recfibo(5))
By inserting this code in an external file named for example file.m, and executing it through octave file.m an error occurs:
warning: function name 'recfibo' does not agree with function filename
'/Users/admin/Google Drive/file.m'
error: 'n' undefined near line 2 column 8 error: called from
octave at line 2 column 3
How should I resolve this particular problem?
Add 1; as the first line of the file:
1;
function fibo = recfibo(n)
if ( n < 2 )
fibo = n;
else
fibo = recfibo(n-1) + recfibo(n-2);
endif
endfunction
disp(recfibo(5))
Any M-file that starts with a function definition is a function M-file, not a script M-file. By adding a meaningless statement to the top, you turn it into a script.
In MATLAB (since fairly recently), a script M-file can define functions at the end of the script. There you'd put the disp line at the top of the file, and have the function block at the end, without any script lines after it. However, Octave requires functions to be defined before you use them, hence it has to come before the script line that uses the function. Octave allowed the definition of functions within a script file before MATLAB introduced that feature, hence their implementation is not compatible with that of MATLAB.
As stated in the answer provided by #CrisLuengo here you have created a function file instead of a script file and they are treated differently in Octave. Because it is a function file Octave executes it by calling the function it defines with no arguments and nargout = 0. So you will get an error that n is undefined.
Another problem is that the function name 'recfibo' does not agree with function filename 'file'. In such cases Octave internally changes the name of the function to the name of the function file so the name is changed to 'file'. Therefor Octave and the function itself will forget the original function name and unfortunately the function cannot call itself recursively!
I like the #CrisLuengo 's answer but I think the more idiomatic and preferable way is always using function files instead of script files, though the script file solution is the only solution that works in previous Octave versions (Octave 3.X).
You can change your code to:
function file
disp(recfibo(5))
endfunction
function fibo = recfibo(n)
if ( n < 2 )
fibo = n;
else
fibo = recfibo(n-1) + recfibo(n-2);
endif
endfunction
I got a problem with running Octave function (ODE), I've tried already present solutions for this problem but nothing is working. I've also tried by saving my filename as egzamin.m but it too not worked.
Code from octave :
function dx=egzamin(x,t)
dx=zeros(4,1);
b=0;
g=9.81;
x1=x(1);
y1=x(2);
Vx=x(3);
Vy=x(4);
dx(1)=Vx;
dx(2)=Vy;
dx(3)=-b*Vx*sqrt(Vx.^2+Vy.^2);
dx(4)=-b*Vy*sqrt(Vx.^2+Vy.^2)-g;
endfunction
N=mod(291813,100);
x1=0;
y1=0;
Vx=20+N;
Vy=20+N;
t=0:0.01:500;
sol=lsode("egzamin",[x1,y1,Vx,Vy],t);
plot(sol(:,1),sol(:,2))
The error is :
error: 'x' undefined near line 5 column 4
error: called from
egzamin at line 5 column 3
Since the file starts with function, it is not a script file,
as explained in the doc:
Unlike a function file, a script file must not begin with the keyword
function
Add any statement (even dummy like 1;) before the function line to get a script file.
# dummy statement to get a script file instead of a function file
1;
function dx=egzamin(x,t)
g = 9.81;
Vx = x(3);
Vy = x(4);
dx = [Vx, Vy, 0, -g];
endfunction
N=mod(291813,100);
x1=0;
y1=0;
Vx=20+N;
Vy=20+N;
t=0:0.01:500;
sol=lsode("egzamin",[x1,y1,Vx,Vy],t);
plot(sol(:,1),sol(:,2))
A very clear explanation of what's going on is given here.
You need to save the function (thus from function to endfunction and naught else) as egzamin.m, and then execute the rest of the code in a script or at the command line. Alternatively, provided Octave does that the same as what MATLAB does nowadays, first put your script (N=(..) to plot()) and then the function.
This is necessary since you are defining your function first, so it doesn't have any inputs yet, as you don't define them until later. The function needs to have its inputs defined before it executes, hence you need to save your function separately.
You can of course save your "script" bit, thus everything which is currently below your function declaration, as a function as well, simply don't give it in- and outputs, or, set all the input parameters here as well. (Which I wouldn't do as it's the same as your
egzamin then.) e.g.
function []=MyFunc()
N=mod(291813,100);
x1=0;
y1=0;
Vx=20+N;
Vy=20+N;
t=0:0.01:500;
sol=lsode("egzamin",[x1,y1,Vx,Vy],t);
plot(sol(:,1),sol(:,2))
endfunction
As a homework assignment, I'm writing a code that uses the bisection method to calculate the root of a function with one variable within a range. I created a user function that does the calculations, but one of the inputs of the function is supposed to be "fun" which is supposed to be set equal to the function.
Here is my code, before I go on:
function [ Ts ] = BisectionRoot( fun,a,b,TolMax )
%This function finds the value of Ts by finding the root of a given function within a given range to a given
%tolerance, using the Bisection Method.
Fa = fun(a);
Fb = fun(b);
if Fa * Fb > 0
disp('Error: The function has no roots in between the given bounds')
else
xNS = (a + b)/2;
toli = abs((b-a)/2);
FxNS = fun(xns);
if FxNS == 0
Ts = xNS;
break
end
if toli , TolMax
Ts = xNS;
break
end
if fun(a) * FxNS < 0
b = xNS;
else
a = xNS;
end
end
Ts
end
The input arguments are defined by our teacher, so I can't mess with them. We're supposed to set those variables in the command window before running the function. That way, we can use the program later on for other things. (Even though I think fzero() can be used to do this)
My problem is that I'm not sure how to set fun to something, and then use that in a way that I can do fun(a) or fun(b). In our book they do something they call defining f(x) as an anonymous function. They do this for an example problem:
F = # (x) 8-4.5*(x-sin(x))
But when I try doing that, I get the error, Error: Unexpected MATLAB operator.
If you guys want to try running the program to test your solutions before posting (hopefully my program works!) you can use these variables from an example in the book:
fun = 8 - 4.5*(x - sin(x))
a = 2
b = 3
TolMax = .001
The answer the get in the book for using those is 2.430664.
I'm sure the answer to this is incredibly easy and straightforward, but for some reason, I can't find a way to do it! Thank you for your help.
To get you going, it looks like your example is missing some syntax. Instead of either of these (from your question):
fun = 8 - 4.5*(x - sin(x)) % Missing function handle declaration symbol "#"
F = # (x) 8-4.5*(x-sin9(x)) %Unless you have defined it, there is no function "sin9"
Use
fun = #(x) 8 - 4.5*(x - sin(x))
Then you would call your function like this:
fun = #(x) 8 - 4.5*(x - sin(x));
a = 2;
b = 3;
TolMax = .001;
root = BisectionRoot( fun,a,b,TolMax );
To debug (which you will need to do), use the debugger.
The command dbstop if error stops execution and opens the file at the point of the problem, letting you examine the variable values and function stack.
Clicking on the "-" marks in the editor creates a break point, forcing the function to pause execution at that point, again so that you can examine the contents. Note that you can step through the code line by line using the debug buttons at the top of the editor.
dbquit quits debug mode
dbclear all clears all break points
I'm new to Matlab and I'm trying to write custom function in matlab that would take function handle as one of its arguments.
I'm getting this error all the time:
Error using subsindex
Function 'subsindex' is not defined for values of class 'function_handle'.
Trying to debug I performed following test: I run command x = fminbnd(#humps, 0.3, 1). I proceeded as expected - I got result x = 0.6370.
So I created custom function called train and I copied ALL the code of function fminbnd to the file train.m. The only thing that I changed is the name, so that code of functions fminbnd and train is now identical except for the names.
Now I run both functions with the same argument and the custom function throws error while original fminbnd returns correct answer.
Here is the code:
>> x = fminbnd(#humps, 0.3, 1)
x =
0.6370
>> x = train(#humps, 0.3, 1)
Error using subsindex
Function 'subsindex' is not defined for values of class 'function_handle'.
Here is header of function train (everything else is copied from fminbnd):
function [xf,fval,exitflag,output] = train(funfcn,ax,bx,options,varargin)
Where is the problem?
Doing a which train showed me that there is a function in the neural network toolbox of the same name.
/Applications/MATLAB_R2009b.app/toolbox/nnet/nnet/#network/train.m % network method
You may be running the nnet train.m rather than the one you think you're running. Are you in the directory containing your train.m? When I made sure I was in the right directory, I got it to work:
>> which train
/Users/myuserid/train.m
>> x = train(#humps,0.3,1)
x =
0.6370
Maybe you can name your file something else like myfminbnd.m instead?
Instead of duplicating the whole fminbnd function, try:
function varargout = myfminbnd(varargin)
varargout = cell(1,nargout(#fminbnd));
[varargout{:}] = fminbnd(varargin{:});
end
this will work as an "alias" to the existing function:
>> fminbnd(#(x)x.^3-2*x-5, 0, 2)
ans =
0.8165
>> myfminbnd(#(x)x.^3-2*x-5, 0, 2)
ans =
0.8165
(you can get the other output arguments as well)