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Quantity Table

Introduction

Quantity tables are 2-dimensional tables with quantity data of the same type. In a sense, it acts like a MatrixNxM without the ability to carry out matrix and vector calculations. Hadamard (element-wise) operations on quantity tables are supported.

The QuantityTable supports dense storage in a double[] or float[] array, or sparse storage, where values are stored with an integer-based row-column index and a double or float value. Since the sparse storage involves quite some overhead, tables need to have a significant percentage of 0-values (40-50% or more) for using sparse storage to make sense.

Quantity Table operations

A QuantityTable implements the Hadamard interface for element-by-element operations. These include:

  • invertElements(): Invert each element of the table (1/value), where the unit will also be inverted. The inversion of a the elements of a Duration quantity table will result in a quantity table of the same size (number of rows and columns), with a unit if 1/s, corresponding to a Frequency.
  • multiplyElements(QuantityTable other): Multiply all elements of this quantity table with those of another quantity table of the same size (but often representing another quantity).
  • divideElements(QuantityTable other): Divide all elements of this quantity table by those of another quantity table of the same size (but possibly representing another quantity).
  • multiplyElements(Quantity<?, ?> quantity): Multiply all elements of this quantity table with the provided quantity.
  • divideElements(Quantity<?, ?> quantity): Divide all elements of this quantity table by those the provided quantity.

The result of a Hadamard operation on, e.g. a QuantityTable<Duration, Duration.Unit> will typically be a QuantityTable<SIQuantity, SIUnit> since the inverse operation, multiplication or division will result in a QuantityTable with a unit that is unknown on beforehand and cannot be determined by the compiler. In the above example of invertElements for a Duration quantity table, the resulting quantity table can be transformed into a proper QuantityTable<Frequency, Frequency.Unit> matrix using the as(Frequency.Unit.Hz) method.

Furthermore, a quantity table is additive, which means that two tables of the same size and same quantity can be added to and subtracted from each other. Quantity tables also implement the Scalable interface, which exposes the scaleBy(double factor) and divideBy(double factor) methods, scaling the elements of the quantity table by factor, respectively 1.0 / factor.

Transforming the QuantityTable

QuantityTable objects do not implement matrix operations such as determinant, matrix multiplication, etc. If a QuantityTable at some point needs to be used for matrix operations, the asVector and asMatrix methods can transform the QuantityTable into a Matrix or column or row Vector of any of the types. For this, the QuantityTable implements the asMatrix1x1(), asMatrix2x2(), asMatrix3x3(), asMatrixNxN(), asMatrixNxM(), asVector1(), asVector2Row(), asVector2Col(), asVector3Row(), asVector3Col(), asVectorNRow(), and asVectorNCol() methods. After the transformation, the table is available for linear algebra operations.

Reversely, the Matrix or column or row Vector classes can all be turned into a QuantityTable with the asQuantityTable() method.