---
title: vDSP_rmsqv
framework: Kernel
role: symbol
role_heading: Function
platforms: [macOS 10.4+]
path: kernel/1532207-vdsp_rmsqv
---

# vDSP_rmsqv

Calculates the root mean square of a single-precision vector.

## Declaration

```occ
void vDSP_rmsqv(const float *__A, vDSP_Stride __IA, float *__C, vDSP_Length __N);
```

## Parameters

- `__A`: The single-precision real input vector A.
- `__I`: The stride for input vector A.
- `__C`: The single-precision output scalar.
- `__N`: The number of elements to process. If N is zero (0), this function returns NAN.

## Discussion

Discussion This function calculates the root mean square of the first N elements of A and writes the result to C:

The operation is:  C = sqrt(sum(A[n] ** 2, 0 <= n < N) / N); The following code shows an example of using vDSP_rmsqv: let stride = vDSP_Stride(1)

let a: [Float] = [-1.5, 2.25, 3.6,                   0.2, -0.1, -4.3] let n = vDSP_Length(a.count)

var c: Float = .nan

vDSP_rmsqv(a,            stride,            &c,            n)

print(String(format: "RMS %.4f", c)) // Prints "RMS 2.5434".

## See Also

### Vector Reduction Functions

- [vDSP_svesq](kernel/1532179-vdsp_svesq.md)
- [vDSP_svs](kernel/1532174-vdsp_svs.md)