How to use partial derivate in my code?

General Usage
1

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I want to use the partial marked red in the figure to write my own code. The code I want to write is like figure below.
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But an error occurred.
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How can I achieve my code? Thank you for your answer.

2

Welcome to the Julia forum!

Two remarks:

  1. Please do share code as text enclosed in triple backticks like ``` and not as screenshots.
  2. Please share a complete example, including the using statements and example input data.

This makes it much easier for others to reproduce your problem.

Also helpful: the output of:

versioninfo()
3

The main issue here is

julia> ∂
ERROR: UndefVarError: `∂` not defined in `Main`
Suggestion: check for spelling errors or missing imports.

So you need to figure out where is the API ∂ from.

If you want to imitate some standard reference, you need to have a better understanding of it. (I have no idea where is the simplified-Chinese-Annotated code snippet from. It appears to be not self-contained.)

4

If you just want to know how to type it, the REPL help tells you:

help?> ∂
"∂" can be typed by \partial<tab>

This kind of tab completion is supported in the REPL and can also be configured in most modern editors.

But by default, ∂ doesn’t have any definition in Julia, and is just another possible identifier, like x or f. It is up to you to assign a meaning to it.