Why are the attached .mat files not matrices? What are these files?

Hello. I recently went onto the following website to obtain matrices to use for descriptor state-space equations. https://morwiki.mpi-magdeburg.mpg.de/morwiki/index.php/RCL_Circuit_Equations I have also attached the data to this question.

However, I do not receive a matrix when I load them into MATLAB. I recieve a data structure that I am unfamiliar with:

As you can see at the right, the A data is just shown as a "val". Now, I do not understand what the val is telling me. I was expecting a 306x306 matrix, but I have 2*306 pairs, such as (134,1) and (230,1) for each value 1-306.

Does anyone know what this data is? How may I use it as a matrix?

• Thank you

Answer 1

[Steven Lord]

A, B, and E are sparse matrices. Only the non-zero elements and the row and column indices of those non-zero elements are stored (and displayed.) So from your example, we know that element (134, 1) of A is 1. We also know that the first 133 rows of the first column of A contain 0. If they had a non-zero value they would have been displayed before element (134, 1).

If only a small percent of the elements in a matrix are non-zero storing those "boring" 0 values could consume a lot of memory and operating on them could consume a lot of time.

[Justin Burzachiello]

Great. Thank you, Steven. This helps me understand the syntax.