Why can't I write this row vector?
显示 更早的评论
I simply want a 1x3 row vector like this: 
. I tried the following:
. I tried the following:[x(1,3); x(2,3); x(3,3)]
but I got the following error:
Unrecognized function or variable 'x'.
Why? How to sort it out?
采纳的回答
John D'Errico
2020-3-22
编辑：John D'Errico
2020-3-22
Very often, people who are just starting to use MATLAB, think that if you don't know the value of something, then it must be symbolic. That is not always true. I'll give some examples later. But to do what you are asking right now, just do this:
X = sym('X',[1,3])
X =
[X1, X2, X3]
As I said, you can have an unknown that will then be estimated. For example, if we stay in the purely numerical domain, we can solve for an unknown vector. This eample is pretty simple, but...
fun = @(X) sum((X - [1 2 3]).^2);
Xinit = [4 4 4];
Xfinal = fminsearch(fun,Xinit)
Xfinal =
0.99999144502901 1.99997109582809 2.99995541073201
Of course, the minimum arises at the vector [1 2 3].
更多回答（1 个）
Image Analyst
2020-3-22
Define x somehow before that line, like these examples
x = magic(3)
x = rand(3)
x = randi(100, 3, 3)
or whatever.
3 个评论
Armando MAROZZI
2020-3-22
Image Analyst
2020-3-22
编辑：Image Analyst
2020-3-22
I don't have that toolbox so I don't know what kind of assumptions it makes. I've added it to the product list, which you forgot to do when you created this posting.
What are you going to do after that? How are you going to use x? Or that 3 element, 1-D column vector you're trying to make from the 2-D x matrix?
Armando MAROZZI
2020-3-22
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