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# cblas_ctrsv(_:_:_:_:_:_:_:_:_:)

Solves a triangular system of equations with a single value for the right side.

```
func cblas_ctrsv(_ ORDER: CBLAS_ORDER, _ UPLO: CBLAS_UPLO, _ TRANSA: CBLAS_TRANSPOSE, _ DIAG: CBLAS_DIAG, _ N: __LAPACK_int, _ A: OpaquePointer?, _ LDA: __LAPACK_int, _ X: OpaquePointer?, _ 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`

The order of matrix `A`.

`A`

Triangular matrix `A`.

`LDA`

The leading dimension of matrix `A`.

`X`

The vector `X`.

`INCX`

Stride within `X`. For example, if `incX` is 7, every 7th element is used.

## Discussion

Solves `A*x=b` or `A'*x=b` where `x` and `b` are elements in `X` and `B`.

> 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.

---

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