Undefined function or variable

Dear All,

I am trying to estimate parameters using non-linear least squares. The version of Matlab I am using is R2018a.

My function is stored in a file myfun.m and has the following lines of code.

function F = myfun(x)
F = (y - (1 + x(1)*(x(2)/0.002))*X1 - (1-x(1)^2)*(x(2)/x(3))*X2 - x(4)*X3)

My dataset is a matrix read in as column vectors which includes the column vectors y, X1,X2, and X3 are stored in a file in a data file.

Both the data file and the file containing the code are in this directory: 'D:\Users\Srinivasan Rangan'

When I type pwd, the above directory is displayed as the current directory.

Before estimating the function, I open the dataset and I see all the variables of the dataset under the workspace panel on the right hand side of the screen.

However, when I try to estimate the parameters of the function using

x = lsqnonlin(myfun,x0)

I get the following error message:

undefined function or variable 'y'.

Error in myfun (line 2)
F = (y - (1 + x(1)*(x(2)/0.002))*X1 - (1-x(1)^2)*(x(2)/x(3))*X2 - x(4)*X3)

I do see y as loaded in the right hand panel under workspace.

How can I fix this error and perform my estimation?

Thanks, Srinivasan

Answer 1

[Guillaume]

Function can't see the variables in your main workspace. You have to pass any variable you want to use to the function.

Change your function to:

function F = myfun(x, y, X)
  F = (y - (1 + x(1)*(x(2)/0.002))*X(:,1) - (1-x(1)^2)*(x(2)/x(3))*X(:, 2) - x(4)*X(:,3));
end

Then change the lsqnonlin call to:

X = [X1, X2, X3];   %numbered variables are bad. Use arrays instead
x = lsqnonlin(@(x) myfun(x, y, X), x0);

A better name than X would be better. One that has meaning.

[Srinivasan Rangan]

Thanks so much! This worked very well and I am getting estimates

Answer 2

[Walter Roberson]

y exists in your base workspace, but not in the workspace of your function.

You can either pass y to the function as a parameter, or you can define myfun as an anonymous function after you load y.

https://www.mathworks.com/help/matlab/math/parameterizing-functions.html

[Srinivasan Rangan]

Thanks so much!