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# subtract(multiplication:_:)

Calculates the double-precision element-wise difference of the product of a vector and a scalar value, and a vector.

```
static func subtract<T, U>(multiplication: (a: U, b: Double), _ vector: T) -> [Double] where T : AccelerateBuffer, U : AccelerateBuffer, T.Element == Double, U.Element == Double
```

## Parameters

`multiplication`

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

`vector`

A tuple that contains the vectors `A` and `B` in `D = (A * B) - C`.

## Return Value

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

## Discussion

This function calculates the element-wise product of vector `A` and scalar value `B`, subtracts vector `C` from the product, and writes the result to vector `D`.

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

![A diagram showing the operation of this function. There are four rows. The top row represents the input vector A with three boxes, and the scalar value B with one box. The second row represents the operation that multiplies A and B, with three boxes, as well as the input vector C with three boxes. 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 vector.  ](images/com.apple.accelerate/media-4387380@2x.png)

The following code shows an example of using this function:

```swift
    let a: [Double] = [ 1,  2,  3,  4,  5]
    let b: Double = 10
    let c: [Double] = [ 5,  4,  3,  2,  1]
    
    let d = vDSP.subtract(multiplication: (a, b),
                          c)
    
    // Prints "[5.0, 16.0, 27.0, 38.0, 49.0]".
    print(d)
```

---

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