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**integer****Member**- Registered: 2008-02-21
- Posts: 79

I'm looking for a definition or name for the diagonal from the lower left to the uper right of a matrix,

Example: 2x2 matrix

The diagonal from the upper left to the lower right is identified as "main diagonal".

The trace(*A*) is the sum of the elements along the main diagonal.

The question: Is there a name for the diagonal from the Lower-left to the upper-right?

Or do you have a reference/resource that might have a name for this diagonal?

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**mathsyperson****Moderator**- Registered: 2005-06-22
- Posts: 4,900

I've seen that referred to as the antidiagonal. Not sure how common the usage of that is though.

Why did the vector cross the road?

It wanted to be normal.

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**integer****Member**- Registered: 2008-02-21
- Posts: 79

mathsyperson wrote:

I've seen that referred to as the antidiagonal. Not sure how common the usage of that is though.

**Thank you.**

Searching for "antidiagonal" gave other terms also used:

subsidiary diagonal

secondary diagonal.

Subsidiary diagonal can be confushed with superdiagonal/subdiagonal when refering to tridiagonal matrices.

The "main diagonal" is the "primary diagonal" and the "antidiagonal is the "secondary diagonal".

I like that.

Again, Thank you.

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