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# vDSP_vmsbD

Calculates the double-precision element-wise difference of a vector and the product of two vectors, using the specified stride.

```
extern void vDSP_vmsbD(const double *__A, vDSP_Stride __IA, const double *__B, vDSP_Stride __IB, const double *__C, vDSP_Stride __IC, double *__D, vDSP_Stride __ID, vDSP_Length __N);
```

## Parameters

`__A`

The input vector `A` in `D = (A * B) - C`.

`__IA`

The distance between the elements in the input vector `A`.

`__B`

The input vector `B` in `D = (A * B) - C`.

`__IB`

The distance between the elements in the input vector `B`.

`__C`

The input vector `C` in `D = (A * B) - C`.

`__IC`

The distance between the elements in the input vector C.

`__D`

The output vector `D` in `D = (A * B) - C`.

`__ID`

The distance between the elements in the output vector `D`.

`__N`

The number of elements that the function processes.

## Discussion

This function calculates the products of the first `N` elements of `A` and `B`, subtracts each product from the corresponding value in `C`, and writes the result to `D`.

```swift
 for (n = 0; n < N; ++n)
    D[n] = (A[n] * B[n]) - C[n];
```

![A diagram showing the operation of this function. There are four rows. The top row represents the input vectors, A and B, with three boxes of each. The second row represents the operation that multiplies A and B, as well as the input vector C, with three boxes of each. The third row represents the subtraction operation as three boxes.  The bottom row represents the output vector D as three boxes. The diagram has connecting lines from the input vectors to the operations, and from the operations to the output vectors.  ](images/com.apple.accelerate/media-4336987@2x.png)

The following code shows an example of using this function:

```swift
    let stride = 1
    let count = 5
    
    let a: [Double] = [ 1,  2,  3,  4,  5]
    let b: [Double] = [10, 20, 30, 40, 50]
    let c: [Double] = [ 5,  4,  3,  2,  1]
    
    let d = [Double](unsafeUninitializedCapacity: count) {
        buffer, initializedCount in
        
        vDSP_vmsbD(a, stride,
                   b, stride,
                   c, stride,
                   buffer.baseAddress!, stride,
                   vDSP_Length(count))
        
        initializedCount = count
    }
    
    // Prints "[5.0, 36.0, 87.0, 158.0, 249.0]".
    print(d)
```

---

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