---
name: "slangb"
section: "3"
platform: "linux"
package: "lapack-doc"
version: "3.12.1-2"
release: "Arch Linux 2026-11-01"
platforms: ["linux"]
url: "https://new.carta.tech/slangb.f"
---

# slangb(3)

Part of [slangb.f(3)](/slangb.f/3.md).

## NAME

SRC/slangb.f

## SYNOPSIS

### Functions/Subroutines

real function **slangb** (norm, n, kl, ku, ab, ldab, work)\
 **SLANGB** returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of general band matrix.

## Function/Subroutine Documentation

### real function slangb (character norm, integer n, integer kl, integer ku, real, dimension( ldab, \* ) ab, integer ldab, real, dimension( \* ) work)

**SLANGB** returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of general band matrix.

**Purpose:**

```
!>
!> SLANGB  returns the value of the one norm,  or the Frobenius norm, or
!> the  infinity norm,  or the element of  largest absolute value  of an
!> n by n band matrix  A,  with kl sub-diagonals and ku super-diagonals.
!>
```

**Returns**

SLANGB

```
!>
!>    SLANGB = ( max(abs(A(i,j))), NORM = 'M' or 'm'
!>             (
!>             ( norm1(A),         NORM = '1', 'O' or 'o'
!>             (
!>             ( normI(A),         NORM = 'I' or 'i'
!>             (
!>             ( normF(A),         NORM = 'F', 'f', 'E' or 'e'
!>
!> where  norm1  denotes the  one norm of a matrix (maximum column sum),
!> normI  denotes the  infinity norm  of a matrix  (maximum row sum) and
!> normF  denotes the  Frobenius norm of a matrix (square root of sum of
!> squares).  Note that  max(abs(A(i,j)))  is not a consistent matrix norm.
!>
```

**Parameters**

*NORM*

```
!>          NORM is CHARACTER*1
!>          Specifies the value to be returned in SLANGB as described
!>          above.
!>
```

*N*

```
!>          N is INTEGER
!>          The order of the matrix A.  N >= 0.  When N = 0, SLANGB is
!>          set to zero.
!>
```

*KL*

```
!>          KL is INTEGER
!>          The number of sub-diagonals of the matrix A.  KL >= 0.
!>
```

*KU*

```
!>          KU is INTEGER
!>          The number of super-diagonals of the matrix A.  KU >= 0.
!>
```

*AB*

```
!>          AB is REAL array, dimension (LDAB,N)
!>          The band matrix A, stored in rows 1 to KL+KU+1.  The j-th
!>          column of A is stored in the j-th column of the array AB as
!>          follows:
!>          AB(ku+1+i-j,j) = A(i,j) for max(1,j-ku)<=i<=min(n,j+kl).
!>
```

*LDAB*

```
!>          LDAB is INTEGER
!>          The leading dimension of the array AB.  LDAB >= KL+KU+1.
!>
```

*WORK*

```
!>          WORK is REAL array, dimension (MAX(1,LWORK)),
!>          where LWORK >= N when NORM = 'I'; otherwise, WORK is not
!>          referenced.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **122** of file **slangb.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.