### Subroutine Question: DSYEV; Eigensolver for Symmetric Matrix

Posted:

**Wed Jan 11, 2006 1:58 am**Hello.

Is this forum the place for posting questions regarding specific routines, or should questions be sent to a specific individual?

My question:

I am looking over the code for DSYEV, a driver routine for solving for the eigenvalues and eigenvectors of a real, symmetric matrix. One of the parameters passed into DSYEV is UPLO. I am not clear on the purpose of this variable. The comments state the following:

“If UPLO = ‘U’, the leading NxN upper triangular part of A contains the upper triangular part of the matrix A. If UPLO = ‘L’, the leading NxN lower triangular part of A contains the lower triangular part of the matrix A. “

So the upper part of the matrix contains the upper part of the matrix, and the lower part of the matrix contains the lower part of the matrix?!?! That would seem obvious, so maybe I am just misunderstanding this variable. Somebody please clarify for me.

Is this forum the place for posting questions regarding specific routines, or should questions be sent to a specific individual?

My question:

I am looking over the code for DSYEV, a driver routine for solving for the eigenvalues and eigenvectors of a real, symmetric matrix. One of the parameters passed into DSYEV is UPLO. I am not clear on the purpose of this variable. The comments state the following:

“If UPLO = ‘U’, the leading NxN upper triangular part of A contains the upper triangular part of the matrix A. If UPLO = ‘L’, the leading NxN lower triangular part of A contains the lower triangular part of the matrix A. “

So the upper part of the matrix contains the upper part of the matrix, and the lower part of the matrix contains the lower part of the matrix?!?! That would seem obvious, so maybe I am just misunderstanding this variable. Somebody please clarify for me.