Is it possible in Matlab to create function handle that will take as input another function handle and how?
e.g. I have h = #(x) x^2
I want to have h as parameter and get as output function that 4*x^2
function alpha = fun(h, type)
x= sym('x',[8,1]);
gamma = 16;
alpha_ = gamma*h(x);
alpha = matlabFunction(alpha_, 'vars', {x});
end
Is it possible to create something like that? I want to avoid creating alphas for multiple function handles.
Related
I have a task to write a function that has an optional output argument.
Let's say I have a function y = fun(a,b). From what I understood, depending on whether the user needs the value y, it will EITHER calculate y OR draw some diagram.
So I think it means that if user calls my function like this: z = fun(1,2), then it calculates y and returns it, but if he calls it like this: fun(3,4);, then it won't return anything and draw a diagram instead.
Is there any way to check how my function has been called inside it? If yes, then how?
You can use nargout here:
function y = q61527462(a,b)
if nargout > 0
% Calculate y
y = a + b;
else
% Plot
plot(a,b)
end
end
so when you call the function as:
>> y = q61527462(1,2)
you get:
y =
3
and when you call with:
>> q61527462(1,2)
you get the plot
Have a look at nargout, that roughly translates to number of argument to output (there is also a nargin to check the number of input arguments).
However, the function will return the return-value anyway if your just check for nargin. You will also need to use varargout (variable argument output) to make your function return something only if the output will be assigned to some external variable.
So you just write in your function
function varargout = fun()
if nargout % implicit cast to a logical. It is equivalent to nargout > 0
% return output
varargout{1} = true; % note that this requires to wrap your output in a cell
else
% do plotting
end
EDIT:
It is even not necessary to use varargout. If you don't assign a value to a return-variable, it won't appear. So MATLAB can manage a not-assigned return-variable (something I was surprised to learn myself^^). This even works with multiple outputs!
In Matlab some functions adapt their output to the number of output variables in the call. For example I can do:
A=[[1 2 3];[4 5 6]];
s=size(A);
And I get
s=[2, 3];
But if I want to handle independently width and height I can do:
[h, w]=size(A);
And I get:
h=2;
w=3;
Now, if I have a function that always output a vector of let's say 3 elements. Is there a way to assign each element to a different variable?
I mean to avoid an scenery like this:
pos=getPosition();
X=pos(1);
Y=pos(2);
Z=pos(3);
I hope I have explained what I mean.
I've had the same problem. Mostly with functions handling coordinates as in your example. My solution was to create the following function:
function varargout = dealOneByOne(vector)
% Assign each column of vector to each variable on the output variables
%
for i=1:size(vector,2)
varargout{i}=vector(:,i);
end
end
Then you can just do
[X,Y,Z]=dealOneByOne(getPosition());
I'm not aware of a simpler way to do it.
Let's define a test function as follows:
function x = test()
x = [1 2 3];
end
Given the function above, this is what I would normally perform in order to split the output array into many distinct variables:
out = num2cell(test());
[a,b,c] = deal(out{:});
A wrapper function can be defined in order to avoid spreading the above assignment into multiple lines:
[a,b,c] = vout_num(test());
function varargout = vout_num(x)
C = num2cell(x);
varargout = C(:).';
end
In your example, the wrapper function would be used as follows:
[X,Y,Z] = vout_num(getPosition());
I have a set of functions such that I want to apply each of them in a separate iteration. I label the functions as: Strategy1(x), Strategy2(x)....Strategy100(x). As you can see, there is a numeric variable in the name of the function. I want to achieve something like
LS = [Strategy1(x),Strategy2(x),...,Strategy100(x)];
Y = zeros(100,1);
for i = 1:1:100
Y(i) = Strategyi(x);
end
I wonder if there is a way to achieve this goal in matlab?
You could create function handles by using str2func
n = 100;
Y = zeros(n,1);
for i = 1:n
funcH = str2func( sprintf('Strategy%d', i));
Y(i) = funcH(x);
end
If you want to concatenate the function names outside the for loop you could use srtcat
strcat('Strategy', strread( num2str(1:n), '%s'))
Hey I'm having trouble integrating a function in MATLAB, constantly getting errors. I'm trying to fill a matrix with the function. exp(x-1)*x^j+k
I2 = zeros(26,3);
k = [0.13, 0.0024, 0.000035];
for i = 1:length(k)
for j = 0:25
fun = #(x,j) exp(x-1).*x.^j+k(i);
I2(j,i) = integral(fun,0,1);
end %end j-loop
end %end i-loop
display(I2);
Thanks.
In the current form the function handle is expecting two inputs but you want a function with a single input for integral. Changing your function handle definition to the following should fix this.
fun = #(x) exp(x-1)*x^j+k(i);
So I have these two made up .m files. This is an example of the problem I'm having and the math is pseudo-math
rectangle.m:
function [vol, surfArea] = rectangle(side1, side2, side3)
vol = ...;
surfArea = ...;
end
ratio.m:
function r = ratio(f,constant)
% r should return a scaled value of the volume to surface area ratio
% based on the constant provided.
% This line doesn't work but shows what I'm intending to do.
[vol,surfArea] = f
r = constant*vol*surfArea;
end
What I'm unsure how to do is pass the rectangle function as f and then access vol and surfArea from within the ratio function. I've read and the Mathworks page on function handles and function functions and have come up empty handed on figuring out how to do this. I'm new to MATLAB so that doesn't help either.
Let me know if you need anymore info.
Thanks!
The correct way of passing the function rectangle as and argument of ratio is
r = ratio( #recangle, constant )
You can then call [vol,surfArea] = f(s1,s2,s3) from within ratio, but it requires the sideX arguments to be known.
If ratio should not require to know these arguments, then you could create an object function and pass this as a reference argument. Or better, you could create a rectangle class altogether:
classdef Rectangle < handle
properties
side1, side2, side3;
end
methods
% Constructor
function self = Rectangle(s1,s2,s3)
if nargin == 3
self.set_sides(s1,s2,s3);
end
end
% Set sides in one call
function set_sides(self,s1,s2,s3)
self.side1 = s1;
self.side2 = s2;
self.side3 = s3;
end
function v = volume(self)
% compute volume
end
function s = surface_area(self)
% compute surface area
end
function r = ratio(self)
r = self.volume() / self.surface_area();
end
function r = scaled_ratio(self,constant)
r = constant * self.ratio();
end
end
end
While I didn't bring this up in my question above, this is what I was searching for.
So what I wanted to do was pass some of rectangles arguments to ratio while being able to manipulate any chosen number of rectangles arguments from within the ratio function. Given my .m files that above, a third .m would look something like this. This solution ended up using MATLAB's anonymous functions.
CalcRatio.m:
function cr = calcRatio(length)
% Calculates different volume to surface area ratios given
% given different lengths of side2 of the rectangle.
cr = ratio(#(x) rectangle(4,x,7); %<-- allows the 2nd argument to be
% manipulated by ratio function
end
ratio.m:
function r = ratio(f,constant)
% r should return a scaled value of the volume to surface area ratio
% based on the constant provided.
% Uses constant as length for side2 -
% again, math doesnt make any sense, just showing what I wanted to do.
[vol,surfArea] = f(constant);
r = constant*vol*surfArea;
end