---
title: "cblas_dtrmv(_:_:_:_:_:_:_:_:_:)"
framework: accelerate
role: symbol
role_heading: Function
path: "accelerate/cblas_dtrmv(_:_:_:_:_:_:_:_:_:)"
---

# cblas_dtrmv(_:_:_:_:_:_:_:_:_:)

Multiplies a triangular matrix by a vector.

## Declaration

```swift
func cblas_dtrmv(_ ORDER: CBLAS_ORDER, _ UPLO: CBLAS_UPLO, _ TRANSA: CBLAS_TRANSPOSE, _ DIAG: CBLAS_DIAG, _ N: __LAPACK_int, _ A: UnsafePointer<Double>?, _ LDA: __LAPACK_int, _ X: UnsafeMutablePointer<Double>?, _ INCX: __LAPACK_int)
```

## Parameters

- `ORDER`: Specifies row-major (C) or column-major (Fortran) data ordering.
- `UPLO`: Specifies whether to use the upper or lower triangle from the matrix. Valid values are 'U' or 'L'.
- `TRANSA`: Specifies whether to use matrix A ('N' or 'n') or the transpose of A ('T', 't', 'C', or 'c').
- `DIAG`: Specifies whether the matrix is unit triangular. Possible values are 'U' (unit triangular) or 'N' (not unit triangular).
- `N`: Order of matrix A.
- `A`: Triangular matrix A.
- `LDA`: Leading dimension of matrix A.
- `X`: Vector X.
- `INCX`: Stride within X. For example, if incX is 7, every 7th element is used.

## Discussion

Discussion Multiplies A*X or A'*X, depending on the value of TransA. important: Apple provides the BLAS and LAPACK libraries under the Accelerate framework to be in line with LAPACK 3.9.1. Starting with iOS 26, iPadOS 26, macOS 26, tvOS 26, visionOS 26, and watchOS 26, the libraries are in line with LAPACK 3.12.0. These new interfaces provide additional functionality, as well as a new ILP64 interface. To use the new interfaces, define ACCELERATE_NEW_LAPACK before including the Accelerate or vecLib headers. For ILP64 interfaces, also define ACCELERATE_LAPACK_ILP64. For Swift projects, specify ACCELERATE_NEW_LAPACK=1 and ACCELERATE_LAPACK_ILP64=1 as preprocessor macros in Xcode build settings under Apple Clang - Preprocessing > Preprocessor Macros.

## See Also

### Double-precision float matrix functions

- [cblas_dasum(_:_:_:)](accelerate/cblas_dasum(_:_:_:).md)
- [cblas_daxpy(_:_:_:_:_:_:)](accelerate/cblas_daxpy(_:_:_:_:_:_:).md)
- [cblas_dcopy(_:_:_:_:_:)](accelerate/cblas_dcopy(_:_:_:_:_:).md)
- [cblas_dgbmv(_:_:_:_:_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dgbmv(_:_:_:_:_:_:_:_:_:_:_:_:_:_:).md)
- [cblas_dgemm(_:_:_:_:_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dgemm(_:_:_:_:_:_:_:_:_:_:_:_:_:_:).md)
- [cblas_dgemv(_:_:_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dgemv(_:_:_:_:_:_:_:_:_:_:_:_:).md)
- [cblas_dger(_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dger(_:_:_:_:_:_:_:_:_:_:).md)
- [cblas_dnrm2(_:_:_:)](accelerate/cblas_dnrm2(_:_:_:).md)
- [cblas_drot(_:_:_:_:_:_:_:)](accelerate/cblas_drot(_:_:_:_:_:_:_:).md)
- [cblas_drotg(_:_:_:_:)](accelerate/cblas_drotg(_:_:_:_:).md)
- [cblas_drotm(_:_:_:_:_:_:)](accelerate/cblas_drotm(_:_:_:_:_:_:).md)
- [cblas_drotmg(_:_:_:_:_:)](accelerate/cblas_drotmg(_:_:_:_:_:).md)
- [cblas_dsbmv(_:_:_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dsbmv(_:_:_:_:_:_:_:_:_:_:_:_:).md)
- [cblas_dscal(_:_:_:_:)](accelerate/cblas_dscal(_:_:_:_:).md)
- [cblas_dspmv(_:_:_:_:_:_:_:_:_:_:)](accelerate/cblas_dspmv(_:_:_:_:_:_:_:_:_:_:).md)