---
name: "dsvdct.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/dsvdct.f"
---

# dsvdct.f(3)

## NAME

TESTING/EIG/dsvdct.f

## SYNOPSIS

### Functions/Subroutines

subroutine **dsvdct** (n, s, e, shift, num)\
 **DSVDCT**

## Function/Subroutine Documentation

### subroutine dsvdct (integer n, double precision, dimension( \* ) s, double precision, dimension( \* ) e, double precision shift, integer num)

**DSVDCT**

**Purpose:**

```
!>
!> DSVDCT counts the number NUM of eigenvalues of a 2*N by 2*N
!> tridiagonal matrix T which are less than or equal to SHIFT.  T is
!> formed by putting zeros on the diagonal and making the off-diagonals
!> equal to S(1), E(1), S(2), E(2), ... , E(N-1), S(N).  If SHIFT is
!> positive, NUM is equal to N plus the number of singular values of a
!> bidiagonal matrix B less than or equal to SHIFT.  Here B has diagonal
!> entries S(1), ..., S(N) and superdiagonal entries E(1), ... E(N-1).
!> If SHIFT is negative, NUM is equal to the number of singular values
!> of B greater than or equal to -SHIFT.
!>
!> See W. Kahan , Report CS41, Computer Science Dept., Stanford University,
!> July 21, 1966
!>
```

**Parameters**

*N*

```
!>          N is INTEGER
!>          The dimension of the bidiagonal matrix B.
!>
```

*S*

```
!>          S is DOUBLE PRECISION array, dimension (N)
!>          The diagonal entries of the bidiagonal matrix B.
!>
```

*E*

```
!>          E is DOUBLE PRECISION array of dimension (N-1)
!>          The superdiagonal entries of the bidiagonal matrix B.
!>
```

*SHIFT*

```
!>          SHIFT is DOUBLE PRECISION
!>          The shift, used as described under Purpose.
!>
```

*NUM*

```
!>          NUM is INTEGER
!>          The number of eigenvalues of T less than or equal to SHIFT.
!>
```

**Author**

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

Definition at line **86** of file **dsvdct.f**.

## Author

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