str2func vectorize input x1, x2 to x

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

Answer 1

[dpb]

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.

Answer 2

[John BG]

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

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Answer 3

[Qun Wu]

You guys are the best.