Anonymous function from for loop

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Gethal
Gethal 2014-10-28
评论： Gethal 2014-10-28
Hello, I am having trouble creating an anonymous function matrix using a for loop. My code looks like this:
n=4; %Or w/e number. Could be 100.
for i = 1:n
f{i,1} = @(x) (x.^i).*(1-x)
end
The output is this:
f =
@(x)(x.^i).*(1-x)
@(x)(x.^i).*(1-x)
@(x)(x.^i).*(1-x)
@(x)(x.^i).*(1-x)
The problem is that the "i" is not changing. It should look like this:
f =
@(x)(x.^1).*(1-x)
@(x)(x.^2).*(1-x)
@(x)(x.^3).*(1-x)
@(x)(x.^4).*(1-x)
Any ideas? Also, I will later have to take the derivative of each row. Is there a simple way to do it? Like this maybe:
derivative(1) = der(f{1})
derivative(2) = der(f{2})
Thanks in advance!

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采纳的回答

Sean de Wolski
Sean de Wolski 2014-10-28
编辑：Sean de Wolski 2014-10-28
Although it is showing i, as the variable, this is actually hardwired to the numeric value.
for ii = 1:n
feval(f{ii},pi)
end
Yields:
ans =
-6.7280
ans =
-21.1367
ans =
-66.4028
ans =
-208.6106
In order to see the value for the captured variables in the anonymous function, you can use functions
fns = functions(f{1})
fns.workspace{1}
In order to take the derivative analytically, I would use Symbolic Math and syms
syms x ix
f = (x.^i).*(1-x)
f =
-x^4*(x - 1)
diff(f,x)
ans =
- 4*x^3*(x - 1) - x^4

更多回答（1 个）

Gethal
Gethal 2014-10-28
Thanks. After doing a lot of research and also reading your answer I have come to a conclusion. I will not use anonymous functions because they don't work well with other MATLAB functions. For example, I cant just multiply an anonymous function by a constant because it says:
Undefined function 'times' for input arguments of type 'function_handle'.
Anonymous functions become too complicated to handle (pun intended). I rather work with other simpler methods. Thanks though. I will look into using symbolic commands. Also thanks for the quick answer.
  2 个评论
Sean de Wolski
Sean de Wolski 2014-10-28
You can multiply the output of anonymous functions
f(1)*f(2)
But since the function requires an input, multiplying it directly doesn't work. It sounds to me like the symbolic approach is the best for your overall use case. Solve everything symbolically and then subs in the values when you need them.

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