[FEATURE] Improved matrix editing UI

I am quite new to mathlive. And I find it not intuitive and user-friendly to do matrix editing, such as

1. adding a column (I get it done by memorizing the keyboard shortcuts)
2. adding a new row for a multi-column matrix only gets one-column row
3. very hard to tell how many columns are there already when most columns are blank

So I suggest

1. add buttons of “new column/row (before/after)” and “remove current column/row” in the virtual keyboard
2. when a new row is added, it spans into multi-column row
3. each blank spot shows ⬚(DOTTED SQUARE) as a placeholder. This will not only make it easy to tell the column-size, but also help user to locate and fill the spot to make a sparse matrix on a mobile device.

[arnog]

After further thoughts, while adding some commands in a virtual keyboard panel is a potential solution, it does have the drawback that the virtual keyboard is not always available (it can be turned off on desktop, for example). So, I don’t think having the default matrix editing commands in the default virtual keyboard is the best option. Instead, I would suggest a floating editing bar (similar to the pop-over in command mode), which would appear when the caret is inside a matrix and would look something like this:

The (+) buttons would allow the insertion of a column/row and the (-) buttons would allow the deletion of a row/column, while the other buttons would allow the selection of the “style” of the matrix.

[arnog]

To clarify, MathLive by default uses the same shortcuts as Mathematica (Ctrl+, and return to add a column/row). I don’t think this issue is about what the shortcuts should be or that MathLive is lacking shortcuts for basic matrix editing.

Note also that it is possible to define a custom virtual keyboard with commands to add/remove columns/rows. If someone wants to submit one, I’d be happy to review it.

The point about having a placeholder visible for empty cells is a good one.

The behavior when inserting a new row could be changed so that a new row has as many columns as the previous one, but note that Latex matrixes are sparse and could have variable number of cells per row. But perhaps that could be not supported when creating a new matrix with MathLive (but still supported if the matrix was pasted into MathLive).