---
name: "langt"
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/langt"
---

# langt(3)

langt: general matrix, tridiagonal

## NAME

langt - langt: general matrix, tridiagonal

## SYNOPSIS

### Functions

real function **clangt** (norm, n, dl, d, du)\
 **CLANGT** returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.  double precision function **dlangt** (norm, n, dl, d, du)\
 **DLANGT** returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.  real function **slangt** (norm, n, dl, d, du)\
 **SLANGT** returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.  double precision function **zlangt** (norm, n, dl, d, du)\
 **ZLANGT** returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.

## Detailed Description

## Function Documentation

### real function clangt (character norm, integer n, complex, dimension( \* ) dl, complex, dimension( \* ) d, complex, dimension( \* ) du)

**CLANGT** returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.

**Purpose:**

```
!>
!> CLANGT  returns the value of the one norm,  or the Frobenius norm, or
!> the  infinity norm,  or the  element of  largest absolute value  of a
!> complex tridiagonal matrix A.
!>
```

**Returns**

CLANGT

```
!>
!>    CLANGT = ( 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 CLANGT as described
!>          above.
!>
```

*N*

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

*DL*

```
!>          DL is COMPLEX array, dimension (N-1)
!>          The (n-1) sub-diagonal elements of A.
!>
```

*D*

```
!>          D is COMPLEX array, dimension (N)
!>          The diagonal elements of A.
!>
```

*DU*

```
!>          DU is COMPLEX array, dimension (N-1)
!>          The (n-1) super-diagonal elements of A.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **105** of file **clangt.f**.

### double precision function dlangt (character norm, integer n, double precision, dimension( \* ) dl, double precision, dimension( \* ) d, double precision, dimension( \* ) du)

**DLANGT** returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.

**Purpose:**

```
!>
!> DLANGT  returns the value of the one norm,  or the Frobenius norm, or
!> the  infinity norm,  or the  element of  largest absolute value  of a
!> real tridiagonal matrix A.
!>
```

**Returns**

DLANGT

```
!>
!>    DLANGT = ( 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 DLANGT as described
!>          above.
!>
```

*N*

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

*DL*

```
!>          DL is DOUBLE PRECISION array, dimension (N-1)
!>          The (n-1) sub-diagonal elements of A.
!>
```

*D*

```
!>          D is DOUBLE PRECISION array, dimension (N)
!>          The diagonal elements of A.
!>
```

*DU*

```
!>          DU is DOUBLE PRECISION array, dimension (N-1)
!>          The (n-1) super-diagonal elements of A.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **105** of file **dlangt.f**.

### real function slangt (character norm, integer n, real, dimension( \* ) dl, real, dimension( \* ) d, real, dimension( \* ) du)

**SLANGT** returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.

**Purpose:**

```
!>
!> SLANGT  returns the value of the one norm,  or the Frobenius norm, or
!> the  infinity norm,  or the  element of  largest absolute value  of a
!> real tridiagonal matrix A.
!>
```

**Returns**

SLANGT

```
!>
!>    SLANGT = ( 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 SLANGT as described
!>          above.
!>
```

*N*

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

*DL*

```
!>          DL is REAL array, dimension (N-1)
!>          The (n-1) sub-diagonal elements of A.
!>
```

*D*

```
!>          D is REAL array, dimension (N)
!>          The diagonal elements of A.
!>
```

*DU*

```
!>          DU is REAL array, dimension (N-1)
!>          The (n-1) super-diagonal elements of A.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **105** of file **slangt.f**.

### double precision function zlangt (character norm, integer n, complex\*16, dimension( \* ) dl, complex\*16, dimension( \* ) d, complex\*16, dimension( \* ) du)

**ZLANGT** returns the value of the 1-norm, Frobenius norm, infinity-norm, or the largest absolute value of any element of a general tridiagonal matrix.

**Purpose:**

```
!>
!> ZLANGT  returns the value of the one norm,  or the Frobenius norm, or
!> the  infinity norm,  or the  element of  largest absolute value  of a
!> complex tridiagonal matrix A.
!>
```

**Returns**

ZLANGT

```
!>
!>    ZLANGT = ( 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 ZLANGT as described
!>          above.
!>
```

*N*

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

*DL*

```
!>          DL is COMPLEX*16 array, dimension (N-1)
!>          The (n-1) sub-diagonal elements of A.
!>
```

*D*

```
!>          D is COMPLEX*16 array, dimension (N)
!>          The diagonal elements of A.
!>
```

*DU*

```
!>          DU is COMPLEX*16 array, dimension (N-1)
!>          The (n-1) super-diagonal elements of A.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **105** of file **zlangt.f**.

## Author

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