# reducemaps.lib

A library providing reduce/map operations in Faust. Its official prefix is rm. The basic idea behind reduce operations is to combine several values into a single one by repeatedly applying a binary operation. A typical example is finding the maximum of a set of values by repeatedly applying the binary operation max.

In this reducemaps library, you'll find two types of reduce, depending on whether you want to reduce n consecutive samples of the same signal or a set of n parallel signals.

### (rm.)parReduce

parReduce(op,N) combines a set of N parallel signals into a single one using a binary operation op.

With parReduce, this reduction process simultaneously occurs on each half of the incoming signals. In other words, parReduce(max,256) is equivalent to parReduce(max,128),parReduce(max,128) : max.

To be used with parReduce, binary operation op must be associative. Additionally, the concept of a binary operation extends to operations that have 2*n inputs and n outputs. For example, complex signals can be simulated using two signals for the real and imaginary parts. In such case, a binary operation would have 4 inputs and 2 outputs.

Please note also that parReduce is faster than topReduce or botReduce for large number of signals. It is therefore the recommended operation whenever op is associative.

#### Usage

_,...,_ : parReduce(op, N) : _


Where:

• op: is a binary operation
• N: is the number of incomming signals (N>0). We use a capital letter here to indicate that the number of incomming signals must be constant and known at compile time.

### (rm.)topReduce

topReduce(op,N) involves combining a set of N parallel signals into a single one using a binary operation op. With topReduce, the reduction process starts from the top two incoming signals, down to the bottom. In other words, topReduce(max,256) is equivalent to topReduce(max,255),_ : max.

Contrary to parReduce, the binary operation op doesn't have to be associative here. Like with parReduce the concept of a binary operation can be extended to operations that have 2*n inputs and n outputs. For example, complex signals can be simulated using two signals representing the real and imaginary parts. In such cases, a binary operation would have 4 inputs and 2 outputs.

#### Usage

 _,...,_ : topReduce(op, N) : _


Where:

• op: is a binary operation
• N: is the number of incomming signals (N>0). We use a capital letter here to indicate that the number of incomming signals must be constant and known at compile time.

### (rm.)botReduce

botReduce(op,N) combines a set of N parallel signals into a single one using a binary operation op. With botReduce, the reduction process starts from the bottom two incoming signals, up to the top. In other words, botReduce(max,256) is equivalent to _,botReduce(max,255): max.

Contrary to parReduce, the binary operation op doesn't have to be associative here. Like with parReduce the concept of a binary operation can be extended to operations that have 2*n inputs and n outputs. For example, complex signals can be simulated using two signals representing the real and imaginary parts. In such cases, a binary operation would have 4 inputs and 2 outputs.

#### Usage

 _,...,_ : botReduce(op, N) : _


Where:

• op: is a binary operation
• N: is the number of incomming signals (N>0). We use a capital letter here to indicate that the number of incomming signals must be constant and known at compile time.

### (rm.)reduce

Reduce a block of n consecutive samples of the incomming signal using a binary operation op. For example: reduce(max,128) will compute the maximun value of each block of 128 samples. Please note that the resulting value, while computed continuously, will be constant for the duration of a block. A new value is only produced at the end of a block. Note also that blocks should be of at least one sample (n>0).

#### Usage

_ : reduce(op, n) : _


Where:

• op: is a binary operation
• n: is the number of consecutive samples in a block.

### (rm.)reducemap

Like reduce but a foo function is applied to the result. From a mathematical point of view: reducemap(op,foo,n) is equivalent to reduce(op,n):foo but more efficient.

#### Usage

_ : reducemap(op, foo, n) : _


Where:

• op: is a binary operation
• foo: is a function applied to the result of the reduction
• n: is the number of consecutive samples in a block.