ND4J Matrix Math

12 August 2016 ~ blog groovy

In my last post (Commons Math - RealMatrix), I discussed the matrix operations support provided by the Apache Commons Math API. In doing my research I also stumbled on a library that is much closer in functionality to the Python NumPy library (commonly used in Machine Learning examples). The ND4J library is a scientific computing library for the JVM, meant to be used in production environments, which means routines are designed to run fast with minimum RAM requirements.

The main draw I had at this point was that their support for array-style element-by-element operations was much deeper than the matrix operations provided by the Apache Commons Math API and much closer to what I was seeing in the Python code I was working with, which makes conversion simpler.

With NumPy in Python you can multiply two arrays such that the result is the multiplication of each value of the array by the corresponding value in the second array. This is not so simple with matrices (as shown in my last post). With ND4J, it becomes much simpler:

def arrA = Nd4j.create([1.0, 2.0, 3.0] as double[])
def arrB = Nd4j.create([2.0, 4.0, 6.0] as double[])
def arrC = arrA.mul(arrB)
println "$arrA + $arrB = $arrC"

will result in:

[1.00, 2.00, 3.00] * [2.00, 4.00, 6.00] = [ 2.00,  8.00, 18.00]

which is as we would expect from the Python case. ND4J also has the ability to do two-dimensional (matrix-style) arrays:

def matA = Nd4j.create([
    [1.0, 2.0, 3.0] as double[],
    [4.0, 5.0, 6.0] as double[]
] as double[][])
println "Matrix: $matA\n"

which will produce:

Matrix: [[1.00, 2.00, 3.00],
 [4.00, 5.00, 6.00]]

All of the other mathematical operations I mentioned in the previous post are available and with data structures that feel a lot more rich and refined for general use. This is barely scratching the surface of the available functionality. Also, the underlying code is native-based and has support for running on CUDA cores for higher performance. This library is definitely one to keep in mind for cases when you have a lot of array and matrix-based operations.

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