How to calculate number of function evaluation used?

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NUR ZAFIRAH MOHD SIDEK 2017-6-20

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编辑： Tamas Kis 2022-12-23

Hi guys, can some one help me to solve my problem?

i've be facing difficulty to find the number of function evaluation. let's say that i have f(x)=x^3+x^2-2 with initial value of x(0)=1.5

i want to calculate x(n+1)=x(n)-(f(x(n)/fprime(x(n))) until n=5

thus, i want to calculate how many time of f(x(n)) have been use until n=5. but if the first iteration has use f(x(1)) then the second iteration also use f(x(1)), it is considered as we only use f(x(1)) one time only.

can someone help me

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KSSV 2017-6-20

What is fprime ?

Jan 2017-6-20

The obvious answer is, that f(x) is called n=5 times.

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Answer 1

Steven Lord 2017-6-20

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If you're using release R2017a or later you could use memoizedFunction. Once you've used memoizedFunction to solve the problem, call stats on it to determine how many times and with which inputs it was called.

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Steven Lord 2017-6-21

Yes, that's how I would do it. The first time you call the function with a new set of inputs, that increments TotalMisses. Each subsequent time you call the function with inputs that are already in the cache, that increments TotalHits.

Tamas Kis 2022-12-23

编辑：Tamas Kis 2022-12-23

Found a way to do this using a handle class: https://www.mathworks.com/matlabcentral/fileexchange/122422-counted-function-countedfunction. In an example I included it is about 5 times faster than using a memoized function.

If you have a function handle f, you can simply do

[f,count] = count_function_calls(f)

and keep using f in the same way as before. When you want to know the number of function calls, you just use

count()

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Answer 2

Torsten 2017-6-20

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When n=5, f and fprime have been called 5 times each, namely to evaluate f(x1),f(x2),...,f(x5), fprime(x1),fprime(x2),...,fprime(x5).

Best wishes

Torsten.

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Torsten 2017-6-20

编辑：Torsten 2017-6-20

在 MATLAB Online 中打开

f=@(x)x^3+x^2-2;
fprime=@(x)3*x^2+2*x;
x=4;
for n=1:5
  x=x-f(x)/fprime(x);
end

Best wishes

Torsten.

NUR ZAFIRAH MOHD SIDEK 2017-6-20

@Jan Simon: ops..sorry..because this is my first time.

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Answer 3

Jan 2017-6-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/345465-how-to-calculate-number-of-function-evaluation-used#answer_271276

在 MATLAB Online 中打开

function fx = f(x)
persistent Count
if isempty(Count)
  Count = 0;
end
if nargin == 0  % Reply counter and reset it
  fx    = Count;
  Count = 0;
  return;
end
fx    = x^3+x^2-2;
Count = Count + 1;
end

Now:

f();
x = f(1) + f(2) + f(3);
Count = f()

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NUR ZAFIRAH MOHD SIDEK 2017-6-21

and is it the same process if i want to find more than one function at the same time?

Jan 2017-6-21

I do not understand you question. This example shows how to insert and request a counter ina function. Of course you can do exactly the same with other functions also.

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