?lagtm

Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

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ID 766686

Date 4/28/2026

Version

Public

?lagtm

Performs a matrix-matrix product of the form C = alpha*A*B+beta*C , where A is a tridiagonal matrix, B and C are rectangular matrices, and alpha and beta are scalars, which may be 0, 1, or -1.

Syntax

call slagtm ( trans , n , nrhs , alpha , dl , d , du , x , ldx , beta , b , ldb )

call dlagtm ( trans , n , nrhs , alpha , dl , d , du , x , ldx , beta , b , ldb )

call clagtm ( trans , n , nrhs , alpha , dl , d , du , x , ldx , beta , b , ldb )

call zlagtm ( trans , n , nrhs , alpha , dl , d , du , x , ldx , beta , b , ldb )

Include Files

mkl.fi

Description

slagtm dlagtm clagtm zlagtm

The routine performs a matrix-vector product of the form:

B := alpha*A*X + beta*B

where A is a tridiagonal matrix of order n , B and X are n -by- nrhs matrices, and alpha and beta are real scalars, each of which may be 0., 1., or -1.

Input Parameters

trans: CHARACTER*1 . Must be ‘N’ or ‘T’ or ‘C’ . Indicates the form of the equations: If trans = 'N' , then B := alpha*A*X + beta*B (no transpose); If trans = 'T' , then B := alpha*A^{T}*X + beta*B (transpose); If trans = 'C' , then B := alpha*A^{H}*X + beta*B (conjugate transpose)
n: INTEGER . The order of the matrix A ( n≥ 0 ).
nrhs: INTEGER . The number of right-hand sides, i.e., the number of columns in X and B ( nrhs≥ 0 ).
alpha , beta: REAL for slagtm / clagtm DOUBLE PRECISION for dlagtm / zlagtm Specify the scalars alpha and beta respectively. alpha must be 0., 1., or -1.; otherwise, it is assumed to be 0. beta must be 0., 1., or -1.; otherwise, it is assumed to be 1.
dl , d , du: REAL for slagtm DOUBLE PRECISION for dlagtm COMPLEX for clagtm DOUBLE COMPLEX for zlagtm . Arrays: dl(n-1), d(n), du(n-1). The array dl contains the ( n - 1) sub-diagonal elements of T . The array d contains the n diagonal elements of T . The array du contains the ( n - 1) super-diagonal elements of T .
x , b: REAL for slagtm DOUBLE PRECISION for dlagtm COMPLEX for clagtm DOUBLE COMPLEX for zlagtm . Arrays: x(ldx,*) contains the n -by- nrhs matrix X . The second dimension of x must be at least max(1, nrhs) . b ( ldb ,*) contains the n -by- nrhs matrix B . The second dimension of b must be at least max(1, nrhs) .
ldx: INTEGER . The leading dimension of the array x ; ldx≥ max(1, n) .
ldb: INTEGER . The leading dimension of the array b ; ldb≥ max(1, n) .

Output Parameters

b: Overwritten by the matrix expression B := alpha*A*X + beta*B

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Developer Reference for Intel® oneAPI Math Kernel Library for Fortran

?lagtm

Syntax

Include Files

Description

Input Parameters

Output Parameters