Evaluate a function with "evalin"

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Kyriacos
Kyriacos 2012-1-10
I am trying to run a function, and for doing so I need some values/ parameters that I have in the base workspace. Can someone tell me why this does not work? How can I fix it?
x0 = [0.5 ; 0.5 ] ;
evalin('base', 'fsolve(@price2T_ss, x0)') ;
[x, fval, exitflag] = evalin('base', 'fsolve(@price2T_ss,x0)') ;
Error message: ??? Undefined function or variable 'yT_y2'.
... where yT_y2 is a parameter that exists and is already defined in the base workspace, but not in the function's workspace.
Thanks a lot!!
Kyriacos

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回答（2 个）

Daniel Shub
Daniel Shub 2012-1-10
This is one of the reasons not to use eval, it makes debugging difficult. I would guess that the price2T_ss function is trying to use yT_y2 and you haven't passed yT_y2 to it. You should also note that I am pretty sure the x0 you are defining in your function workspace is not being by fsolve. Why not just pass yT_y2 to your function so you do not have to do evalin.
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Jan
Jan 2012-1-10
+1. Use EVAL only for these cases:
1. code obfuscation: a kind of tedious copy protection.
2. if you really need to define global variables dynamically: there is no function form like "global('a')"
Btw: avoiding globals is a good programming practize also...
Walter Roberson
Walter Roberson 2012-1-11
There are also some cases having to do with constructing function handles dynamically.

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Walter Roberson
Walter Roberson 2012-1-10
The fsolve() gets invoked within the base workspace, but the price2T_ss gets invoked from fsolve() or one of its subroutines, and so does not have direct access to the base workspace.
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Walter Roberson
Walter Roberson 2012-1-10
Changing fsolve() would not be good enough: you would need to change price2T_ss .
You should consider using nested functions with shared variables rather than going through the base workspace.

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