polyfit error first two inputs must have the same number of elements.

Question

alp onur karacay 2021-11-22

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1593159-polyfit-error-first-two-inputs-must-have-the-same-number-of-elements

回答： Walter Roberson 2021-11-23

hello everyone, i have this error how can i fix it please instead of saying,write the code for it please because i am new in matlab and also my deadline is coming soon Thanks a lot for everything.

1 个评论
显示 -1更早的评论隐藏 -1更早的评论

Image Analyst 2021-11-22

编辑：Image Analyst 2021-11-22

We can't run an image. Post text. I'm not going to rewrite all your homework for you. Make it easy to help you, not hard.

In general if you have polyfit(x, f, 4) then x must have exactly as many elements as f has. Evidently your do not.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Walter Roberson 2021-11-23

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1593159-polyfit-error-first-two-inputs-must-have-the-same-number-of-elements#answer_837874

在 MATLAB Online 中打开

You create a vector x . Then for the function values, you compute

temp = sqrt(1/(1+x.^2))

However, here x is the entire vector, so 1+x.^2 is a vector. You then compute 1 / the vector. However, in MATLAB, the / operator is not the division operator: the / operator is the matrix division operator. When B is a matrix, A/B is similar to A * pinv(B) where the * operator I show here is the algebraic matrix multiplication operator, also known as "inner product" . The operator for doing element-by-element division is the ./ operator -- notice the period.

If you look back to where you calculated x from k values, notice that you used k(i) in your calculation, so you were working with scalars there. You do have a /n in that calculation, but when n is a scalar, pinv(n) is 1 divided by the scalar, so in the expression A/B where B is a scalar, the expression becomes equivalent to A./B -- so your code for building x from k worked out, because you selected one k value to work with at a time. But your newer loop, you did not select one x value at a time.