Message Boards Message Boards

0
|
180 Views
|
7 Replies
|
0 Total Likes
View groups...
Share
Share this post:
GROUPS:

Why does this variable forget its assignment?

Why does $\hat{\beta}$ change values? If possible, I'd like to use math notation for clarity in code like this simplified example.

Attachments:
POSTED BY: Jay Gourley
7 Replies

I suspect you’ll get the expected result shown if you evaluate in separate cells. What you are seeing, I think, is a display error but (I hope) not an error in the actual assignment.

POSTED BY: Daniel Lichtblau

Thanks, Daniel Lichtblau. I get the same unexpected result even when displaying in a separate cell.

POSTED BY: Jay Gourley

Weird: The first time I evaluated it, I got the buggy results. Then I copied some of the pieces and evaluated them separately. The alpha line threw a syntax error. Then I deleted my mess, and reevaluated the four-line cell. Then it worked fine. I quit the kernel and tried again. It worked fine. Maybe there's a parsing error in the original notebook. I didn't edit the first cell, but maybe it got re-parsed correctly.

It won't let me add this notebook: https://www.wolframcloud.com/obj/mroge02/Published/198902202

POSTED BY: Michael Rogers
Posted 12 hours ago

Just for the record, I cannot reproduce the problem at all (14.2.0 on MacOS).

POSTED BY: Eric Rimbey
Posted 11 hours ago

Thanks, Eric Rimbey, for checking. Strangely, I sometimes cannot reproduce it either. When I started this thread, I thought it was consistently reproducible. I now know it occurs sometimes and sometimes doesn't. Unless you believe in software spirits, something I'm doing triggers it. Maybe Michael Rogers (also in this thread) did the same thing. If I figure out what I'm doing that turns this oddity off and on, I'll add that to this thread. If you have ideas, please share. In the meantime, here are two iterations of the same notebook I posted before. No changes were made between the two other than reloading and executing. It's likely another open notebook at the time had altered the kernel for one and not the other.

Attachments:
POSTED BY: Jay Gourley
Posted 8 hours ago

Your new notebook still works fine for me. As for suggestions...

Don't use fancy characters as symbols in your code. If you end up writing a bunch of code that uses that character, it's tedious to type. Just typing a string of alpha characters is so much easier than inputting special characters. I wouldn't mention this at all if you were just using your overhat beta as a formal symbol, but you're assigning it a value, which means you want that symbol to be evaluated to some value every time it's encountered in your code, which suggests you'll be typing that overhat beta multiple times. That just gets so tedious.

You say you like to use "math notation" for clarity, but what I interpret that to mean is that you want what you display to other people to align with what they're familiar with. Clarity comes from understanding what your symbols mean, and you surely know what you intended your symbols to mean. I know I'm being presumptuous here, but I think you'd be better off using convenient symbols (convenient to type and with names you understand) for your code and then use Format or some other mechanism for creating what you will display to others.

I don't know the exact input mechanism you used, but the result is that your overhat beta definition is actually creating a DownValues value for OverHat. One consequence is that if anywhere in your code you assigned a value to plain beta, that would collide with your definition for overhat beta. Other than that, I don't think this should make a difference, but there might be some obscure reason why it's safer to create OwnValues for a symbol rather than DownValues for OverHat. You can use unicode to create an overhat beta that's just a symbol.

Lastly, and this is probably the least helpful, I'd suggest you use CompoundExpression rather than just newlines to separate "lines" of code. I have a vague memory that way back in the day newlines were interpreted as just white space, which then would often be interpreted as multiplication. So you really did need to use ; to separate expressions that you wanted evaluated independently. In recent times, I see lots of Mathematica code with expressions separated only by newlines instead of ;, but I just can't bring myself to break my old habits. I personally think not using ; it makes it very confusing to read notebooks, because you get all these output cells that you have to sort of reverse-collate back to the input code. I seriously doubt that this is causing your problem, but you might give it a try.

POSTED BY: Eric Rimbey
Posted 4 hours ago

When I try, I also get errors in the following way. I started to put Hold[] around each expression and as I did that the editor went completely haywire, the hats moved around, were over the wrong symbols, and so on. The cell got weird. I opened the file in BBEdit and everything looked "normal" in that there were no extra symbols or so in the expressions. Running 14.2 on Apple M1 Macbook.

POSTED BY: Paul Nielan
Reply to this discussion
Community posts can be styled and formatted using the Markdown syntax.
Reply Preview
Attachments
Remove
or Discard

Group Abstract Group Abstract