ERR: INVALID DIM on TI-84 — The Five Causes and Their Fixes

ERR: INVALID DIM tells you that the calculator has been pointed at data whose size it cannot use. The arithmetic is almost never the problem; the shape of the data is. That is why the message appears when you press GRAPH and nothing about the function you typed looks wrong.

It is the classic complaint of “my graph will not draw”. The usual culprit is a statistical plot that was switched on in an earlier lesson and never switched off. The plot still refers to lists, and if those lists have since been cleared, plotting anything fails with ERR: INVALID DIM even though the function itself is faultless.

Understanding which four situations produce the message is the whole of the fix. Three of them are configuration problems that take seconds to correct, and one of them is the trickiest data-entry mistake on the calculator.

What the message actually refers to

The TI reference guide lists four triggers for this message: a stat plot that is switched on while the stat lists contain no values; a list dimension that is not a whole number between 1 and 999; a matrix dimension that is not a whole number between 1 and 99; and an attempt to invert a matrix that is not square. What every one of those has in common is that the size or existence of the data is impossible, not the calculation performed on it.

Arithmetic between data of disagreeing shapes is a separate fault with a separate name, ERR: DIM MISMATCH, which is worth knowing about before you start deleting rows. The DIM MISMATCH page explains where the line between the two messages falls.

Cause 1: a stat plot switched on with lists that hold nothing

Press 2nd Y= to open the STAT PLOT menu and look at the first line. If it reads Plot1...On, one of the three plots is live. A live plot needs list data behind it: a scatter plot or an xyLine plot reads two lists, and a histogram or box plot reads one. When those lists are empty — because they were cleared at the end of a previous topic — the graph screen cannot be drawn at all, and the function in Y= is dragged down with it.

The one-keystroke remedy is on the same menu: choose 4:PlotsOff and press ENTER. That switches all three plots off without touching your lists, and the function graph will work immediately. If you still want the plot, open STAT then 1:Edit and give the plot two lists that contain data of equal length.

One caveat matters here. Two lists of different lengths are not an INVALID DIM problem at all — they raise ERR: DIM MISMATCH the moment an operation combines them. So if switching the plots off does not clear the message, check the lengths before you look anywhere else.

Cause 2: a stray value left below the last real entry

A list on a TI-84 has no declared length. Its dimension is set by the last row that contains anything, so a value typed ten rows below your data extends the list by ten elements and fills the rows in between with zeros. Every plot, mean, standard deviation and regression computed from that list afterwards quietly includes those zeros.

This cause is the hardest to see, because the list looks correct at a glance: the genuine data sits at the top of the column and the stray entry is off screen below it. Running a summary statistic such as 1-Var Stats over the padded list is the quickest way to see the damage, and the standard deviation walkthrough shows which figures to compare.

The safe habit is to press the down arrow once past the last value you entered. If a zero appears under your data, it either belongs there or it should be deleted.

Cause 3: a list or matrix dimension outside the permitted range

Dimensions must be whole numbers. Asking for a list of 3.5 elements, of zero elements, or of more than 999 is rejected immediately. Matrices must be whole numbers from 1 to 99 in each direction, and separately the memory available on the calculator will refuse a matrix of more than 400 cells. Fractional dimensions usually arrive through a calculation that was meant to produce a count but produced an average instead, so check the value you stored before assuming the calculator is faulty.

Cause 4: inverting a matrix that is not square

An inverse only exists for a square matrix, so [A]⁻¹ on a matrix with different numbers of rows and columns is refused with this message. A square matrix whose determinant happens to be zero is a different case again: the shape is valid but the matrix cannot be inverted, and the calculator says ERR: SINGULAR MAT instead. Both are covered in the error code list.

Clearing stray list entries properly

The two keys behave very differently in the list editor, and that difference is the whole technique.

Press STAT and choose 1:Edit. Move the cursor onto the offending value and press DEL. The element is removed and everything below it shifts up one row, so the list genuinely shrinks. This is almost always what you want.

Press CLEAR with the cursor on the list name at the top of the column, and you get the opposite result: the request to clear that entire list. Confirm with ENTER and the column is emptied, which is useful at the end of a topic and destructive in the middle of one.

To empty several lists at once, the ClrList command does the same work from the home screen, reached through the catalogue. It saves opening the editor three times when a data set has spread across L1, L2 and L3.

What this message is not

Two neighbouring messages are routinely blamed for it, and telling them apart saves time.

• ERR: DIM MISMATCH appears when one operation combines data of different shapes: two lists of unequal length handed to a two-list regression, or a matrix product whose inner dimensions do not agree.
• ERR: WINDOW RANGE appears when the window itself cannot be drawn, for example Xmax smaller than Xmin. The graph fails in the same way, but the message names the window rather than the data. Our window settings guide lists the combinations that are rejected.

Fixing it in order

1. Press 2nd STAT PLOT, choose 4:PlotsOff and press ENTER.
2. Press GRAPH again. If the curve appears, a plot was the cause.
3. Open STAT, choose 1:Edit, and scroll to the bottom of every list involved.
4. Press DEL on anything that should not be there, or make the two lists equal in length.
5. Press WINDOW and confirm that Xmin is smaller than Xmax and Ymin is smaller than Ymax.
6. Only if none of that explains the message, reset RAM as TI’s own guidance suggests — and export your programs first, because the reset erases everything held in memory.

If the message survives all six steps, the next place to look is the entry itself. A bracket or comma in the wrong place can hand the calculator a value it cannot use at all, and the diagnosis for that fault is set out on our ERR: SYNTAX page.

Graphing calculators such as the TI-84 Plus and TI-84 Plus CE are allowed on the ACT mathematics test and on the SAT maths questions, so a plot left switched on is a problem worth solving before an exam rather than during one. Rules are revised occasionally, so confirm the current wording with the official board and your teacher.