---
name: "cptt01.f"
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/cptt01.f"
---

# cptt01.f(3)

## NAME

TESTING/LIN/cptt01.f

## SYNOPSIS

### Functions/Subroutines

subroutine **cptt01** (n, d, e, df, ef, work, resid)\
 **CPTT01**

## Function/Subroutine Documentation

### subroutine cptt01 (integer n, real, dimension( \* ) d, complex, dimension( \* ) e, real, dimension( \* ) df, complex, dimension( \* ) ef, complex, dimension( \* ) work, real resid)

**CPTT01**

**Purpose:**

```
!>
!> CPTT01 reconstructs a tridiagonal matrix A from its L*D*L'
!> factorization and computes the residual
!>    norm(L*D*L' - A) / ( n * norm(A) * EPS ),
!> where EPS is the machine epsilon.
!>
```

**Parameters**

*N*

```
!>          N is INTEGER
!>          The order of the matrix A.
!>
```

*D*

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

*E*

```
!>          E is COMPLEX array, dimension (N-1)
!>          The (n-1) subdiagonal elements of the tridiagonal matrix A.
!>
```

*DF*

```
!>          DF is REAL array, dimension (N)
!>          The n diagonal elements of the factor L from the L*D*L'
!>          factorization of A.
!>
```

*EF*

```
!>          EF is COMPLEX array, dimension (N-1)
!>          The (n-1) subdiagonal elements of the factor L from the
!>          L*D*L' factorization of A.
!>
```

*WORK*

```
!>          WORK is COMPLEX array, dimension (2*N)
!>
```

*RESID*

```
!>          RESID is REAL
!>          norm(L*D*L' - A) / (n * norm(A) * EPS)
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **91** of file **cptt01.f**.

## Author

Generated automatically by Doxygen for LAPACK from the source code.