I'm using Scilab and I'm trying to make a function like the following:
function p = binary_search(myf,a,b)
The target is to make a binary_search to find such p that: myf(p) = 0 in [a,b].
I want to do something like this:
root = binary_search("x^3 - 10",1,2)
Where the first string is a definition of a function.
The only way I found is defining a function called x3:
function x = x3(p)
x = p^3 - 10;
endfunction
and then, inside binary_search, do something like:
fa = x3(a);
Any ideas?
Thank You!
If you have defined the function f(x) = x^3 - 10 , either using deff('y=f(x)','y=x^3-10') or the regular "function ... endfunction" syntax, then you can simply pass f as an argument: define
function r = binary_search(f,a,b)
% do the binary search here and store the result in r
endfunction
Then you can call
---> binary_search(f, 1, 2)
which works fine in SciLab.
In MATLAB/octave, the interpreter considers " f " as an equivalent for f(), i.e., it would execute the function f without arguments, which will result in an error "x undefined". To avoid this, you have to type an # in front of f:
---> binary_search( #f, 1, 2) %% in MATLAB/octave
Functions in Scilab can be passed as arguments to other functions. Therefore, if you have one function, f:
function y=f(x)
y = x^3 - 10
endfunction
you are free to pass that to another function,
root = binary_search("x^3 - 10",1,2)
deff is simply a way to quickly define a function- usually inline on the interpreter.
Alternatively, you can also pass an expression as a string to a function and have that evaluated using the evstr command:
function p = binary_search(expression, a, b)
evstr expression
//Rest of your code
endfunction
You would implement this on the interpreter thus:
expression = "a^3 - 10"
root = binary_search(expression, 1, 2)
I found a solution:
In the main window (the interpreter), I define the function like:
deff('[y] = square(x)','y=x^2')
Then, I call
bi(square,0,2)
In the function, I just do 'f(x)':
function [x] = bi(f,a,b)
fa = f(a);
Related
I wrote a function in octave and got an error like this:
parse error near line 6 of file D:\Evan\Kuliah\Smt 4\METNUM\newton_method.m
syntax error
y = #3*x^2 - 4*x;e
code:
function y = df(x)
y = #3*x^2 - 4*x;
end
I've changed the function to something like this
function y = df
y = #3*x^2 - 4*x;
end
but the result remains the same
The # doesn't belong there, without it it should work fine. Also I recommend using the pointwise operators, so you can evaluate the function on whole arrays, otherwise they will be interpreted as matrix operations:
function y = df(x)
y = 3*x.^2 - 4*x;
end
The right syntaxis is:
y= #(x)3x^2-4x
You forgot to write the variable "x" betweent braces after "#".
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)
I have two functions:
function [] = func_one()
S.pb = uicontrol('style','push','unit','pix','posit',[20 20 260 30],
'string','Print Choices','callback',{#func_two,S});
and I have the second function:
function [a] = func_two(varargin)
a = 'alon';
end
I want func_one to return the variable a of func_two. How can I do that please?
I tried:
function [a] = func_one()
But I guess I have to do something with 'callback',{#func_two,S})
Thank you all!
If, as you say, you want func_one to return the value a in func_two then the easiest way to do this without using a callback is:
function [a] = func_one()
S.pb = uicontrol('style','push','unit','pix','posit',[20 20 260 30],
'string','Print Choices');
a = func_two()
The above will allow you to say run a=func_one and a will be the string 'alon'.
If you really really want func_two() to be a callback of your pushbutton, and you want a='alon' to be assigned in the workspace of func_one (the function that calls func_two) then put this in func_two
assignin('caller','a',a)
And if neither is what you want, then maybe you can indicate why you want func_one to return what func_two returns - like the exact interaction you are hoping to have with your GUI and how it differs from what you're actually experiencing.
If you are designing a GUI programmatically, I suggest you use nested functions to share data. Example:
function IncrementExample()
x = 0;
uicontrol('Style','pushbutton', 'String','(0)', ...
'Callback',#callback);
function callback(o,e)
%# you can access the variable x in here
x = x + 1;
%# update button text
set(o, 'String',sprintf('(%d)',x))
drawnow
end
end
helo, I have the following function called stat.m
function [mean,stdev] = stat(x)
n = length(x)
mean = sum(x)/n
stdev = sqrt(sum((x-mean).^2/n))
I defined x as a vector which is [1,2,5,7,9]
how come when I type a = stat(x), matlab returns a = 5 for the last line at command prompt?
If you want to get both return values, you have to do this:
[a, b] = stat(x);
If you just do a = stat(x), MATLAB interprets that to mean that you only want the first return value.
because a gets the first argument mean
try to call it [a,b] = stat(x)