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str2func vectorize input x1, x2 to x

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Qun Wu
Qun Wu 2017-3-16
回答： Qun Wu 2017-3-16
When using str2func, I find that I can do these things such as,
str = 'x(1)^2 + 3*x(2)';
f = str2func(['@(x)' str]);
f([4 5])
and
str1 = 'x + 2*u';
f1 = str2func(['@(x,u)' str1]);
f1(2,3)
However, what I need is something like
str2 = 'x(1) + u - x(2)';
f2 = str2func('@(x,u)', str2);
f2([1,2],3)
which gives me an error "Too many input arguments."
Any suggestions please? Thank you all in advance.
Qun

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采纳的回答

dpb
dpb 2017-3-16
You didn't follow your previous successful pattern...
f1 = str2func(['@(x,u)' str1]);
as written is the concatenation of two strings; you correctly concatenated the argument list to the function in the previous cases but for some reason didn't for the following...
f2 = str2func('@(x,u)', str2);
Simply write like you did f1
f2 = str2func(['@(x,u)' str2]);
and all is well. The error is there were two instead of only one string in the argument list.

更多回答（2 个）

John BG
John BG 2017-3-16
编辑：John BG 2017-3-16
Hi Qun Wu
with the following syntax it works ok
str2 = 'x1 + u - x2'; f2 = str2func(['@(x1,x2,u)', str2]); f2(1,2,3)
the following also works ok
str2 = 'x(1) + u - x(2)'; f2 = str2func(['@(x,u)', str2]);f2([1 2],3)
if you find this answer useful would you please be so kind to mark my answer as Accepted Answer?
To any other reader, please if you find this answer
please click on the thumbs-up vote link
thanks in advance
John BG
<mailto:jgb2012@sky.com jgb2012@sky.com>
Qun Wu
Qun Wu 2017-3-16
You guys are the best.

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