How can I fix undefined function problem

I ran this code on Octave and I got this undefined problem. Can someone help me to solve this?

[KSSV]

f is not entered as input into the function and is being used in the function.

[Minh Nguyen]

I fixed that and now I don't know why "end" is error.

[Jan]

"While" needs to be in lower case.

[Minh Nguyen]

oh thank you very much

[Walter Roberson]

The two phrases beginning with # are invalid syntax.

The second one

#d = -grad nx1

will need to rewritten as it has no operator between the subexpressions. Perhaps

   d = [-grad, nx1]

However this would overwrite the d variable from the first half of the line, and would involve calling the grad() function with no arguments.

[Minh Nguyen]

I know # is invalid in matlab but I use octave, the line beggin with '#' is comment.

[Walter Roberson]

Your grad function is wrong. Correct is

A*x + (x'*A).'

In the case where you restrict x to be real-valued then it simplifies to 2*A*x

[Minh Nguyen]

yes, I got some confusion. Thank you.

[Walter Roberson]

Octave is off-topic here. Unless perhaps you are asking for assistance in converting Octave code to MATLAB, when you ask questions here you are expected to be using only the parts of Octave that are compatible with MATLAB.

Reminder: the purpose of Octave is to bankrupt Mathworks or force them to open-source all products. Seriously.

[Minh Nguyen]

OK. I do not know that. I will ask the follow-up questions carefully.

[Jan]

@Walter Roberson: Is this true? Octave is much slower, less stable and cannot compete with Matlab in science and industrial work. But it is useful for students to learn programming. I have more computers than Matlab licenses so I'm using Octave also without having the intention to bankrupt MathWorks.

[Walter Roberson]

@Jan

Yes. The Free Software Foundation is a political movement designed to force the entire world to get rid of proprietary software. The belief is that since it is inexpensive to copy the source for software that is already written, that it should be mandatory world-wide that the source code should be provided for all executable software, and that everyone should have the right to modify the software. It explicitly believes that all software companies that sell proprietary closed-source software should make the source code for all of their software available, and that all such companies should switch to becoming consulting firms that people hire to customize the code (with the result becoming available to everyone.) Or should go bankrupt. Either make the source code available for anyone to use free, or else go bankrupt, either one is fine with Free Software Foundation.

Free Software Foundation does not produce products such as gcc or octave "out of the goodness of their hearts": FSF produces the products to ruin the market for proprietary software, to try to force the world to give up proprietary closed-source software, because it believes that proprietary closed-source software is morally wrong to exist.

I give away a lot of assistance because I choose to. Free Software Foundation says that if I write software and make it available to anyone else, that I should be required to give away the source to everyone in the world.

[Jan]

This sounds like a religious argumentation. I'm very interested in this topic, but I have to come back to more on-topic discussions in this Matlab forum. Thanks for your explanations.