A very odd loop behavior

Question

Tomas Iesmantas 2013-3-14

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I encountered a quite odd and unseen behavior in "for" loops. Consider this simple loop:

for i=1:5
  Function(rand(1,1))
end

The loop gives the same results, while repeated lines as this:

Function(rand(1,1))
Function(rand(1,1))
Function(rand(1,1))
Function(rand(1,1))
Function(rand(1,1))

Gives 5 different results. What might be the problem? It seems that the "for" loop evaluates the function 5 times with the same argument. This effect is in Wondows, while in Mac system everything goes smoothly and produces different results.

Any advice would be of great value.

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Answer 1

Tomas Iesmantas 2013-3-14

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What I have already figured out, is that since at every step in the "for" loop I create a new .m file and delete previous file, matlab still have a copy of the old file and executes that old .m instead of newly created. To overcome this I wrote a line to clear old .m file from a memory and everything seems to work properly.

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Jan 2013-3-14

Creating M-file dynamically is a bad programming practize. It is much more efficient and less prone to errors to call a static function with changing parameters. Any kind of meta-programming increases the effort for debugging substantially, and in all cases I've seen already, the parameterized functions have been more direct and clear.

Tomas Iesmantas 2013-3-20

In my case the content of the function varies:number of equations, complexity of equation, parameters of that equation. So it is not possible to creat one function and just feed the parameters. However, I found way better solution - creating the function as a string and not printing it to some m file, but converting it to function with matlab function "str2func".

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Answer 2

Wayne King 2013-3-14

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在 MATLAB Online 中打开

We don't know anything about Function(), but that is certainly not the case in Windows in general

for ii = 1:5
     sum([rand(1,1) 0])
 end

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Tomas Iesmantas 2013-3-14

Unfortunately the function is very complex and uses another subfunctions as well as construction of txt files, so it would not be of any use to post it here.