## Overview

Matrices, do you hate them? I do, and they turn up all over the place in the projects I work with. So over time
I have developed a class `CMatrix`

to handle all the things we need, and some I expect to need in the future.

## How the data is handled

First lets take an overview of how the class handles the data. The matrix data is allocated in
a flat array of `double`

s with an integer reference counter at the end of the array. As the matrix is dynamic, we
use a reference count system to avoid efficiency hits when assigning/copying one matrix into another. Two object can point to
the same data, and they only diverge when one of them changes the data, getting its own copy of the data at that point.
The data is only deleted when the last reference to it is being deleted. This has advantages for objects returned by function
calls by value, and which are assigned by `operator=`

, as there is little penalty in assigning a pointer compared to
a `new`

/copy operation.

## Serialization

The `CMatrix`

class inherits directly from `CObject`

and is full serialization compatible.

## CMatrixHelper

A small helper class has been added to allow a simulated `CMatrix::operator[][]`

to work. I stole
this idea shamelessly from **Alex Chirokov**'s article 2D Matrix
Container with [][] indexing. A nice way of doing it. Note also that you should not be creating any objects of this type in your
own code. It is used for this purpose only.

## Robustness

In DEBUG mode, the code compiles with 0 warnings/errors and has extensive **ASSERT**ion checking through out, so it should catch any
problems that you have (or I have) in code. Most of the functionality has been
thoroughly checked, but I would recommend checking your
results, just in case!

## Constructors

You can construct a matrix object using the following methods:

`CMatrix()`

Constructs a 1 * 1 array, this is the default constructor.
`CMatrix(CMatrix& other)`

Copy constructor
`CMatrix(nCols, nRows)`

Constructs a matrix of ` nCols * nRows`

dimensions. All data is 0.
`CMatrix(size, diagonal)`

Constructs a square matrix with or without 1's on the diagonal.
`CMatrix(VARIANT)`

Constructs a ` CMatrix`

object from a 2 dimension
` SAFEFARRAY`

variant.

As a note, any non-initialized matrix elements will be set to 0 on construction.

## Operators overloaded

The following operators have been overloaded:

`operator=(CMatrix)`

For standard assignment.

#### Arithmatic

`operator+(CMatrix)`

Adds 2 matrices together, must be the same size
`operator-(CMatrix)`

Subtracts 1 matrix from another, must be the same size
`operator*(CMatrix)`

Multiples 2 matrices together, the two inner
dimensions must be the same, e.g. 3*2 by 2*3
`operator+=(CMatrix)`

Adds one matrix onto the current matrix, must have same dimensions.
`operator-=(CMatrix)`

Subtracts one matrix from the current matrix, must have same dimensions.
`operator*=(CMatrix)`

Mutiples the current matrix by the other matrix
`operator*=(double)`

Multiples all matrix elements by the given value
`operator*(CMatrix, double)`

Multiples all elements by the given value, returning a new matrix

#### Comparison

`operator==(CMatrix)`

For matrix comparison, returns `true`

if identical, `false`

otherwise.

#### Element access

`operator[](int)`

Works with the class `CMatrixHelper`

to simulate a `operator[][]`

.

## Get/Set functions

Two standard access function are provided.:

`GetElement(nCol, nRow)`

returns the given element value
`SetElement(nCol, nRow, value)`

Sets the given element to a different value

## Other matrix functions

`GetNumColumns()`

Returns the matrices columns dimension
`GetNumRows()`

Returns the matrices rows dimension
`SumColumn(column)`

Returns the sum of all elements in the given column
`SumRow(row)`

Returns the sum of all elements in the given row
`SumColumnSquared(column)`

Same as `SumColumn()`

but the return value is squared
`SumRowSquared(row)`

Same as `SumRow()`

but the return value is squared
`GetNumericRange(min, max)`

Returns the lower and upper values of elements in the matrix
`GetSafeArray()`

Returns a `VARIANT`

with a copy of the
`CMatrix`

data in a `SAFEARRAY`

. Note that the `VARIANT`

should
be cleared using `VariantClear(var)`

unless you pass the `VARIANT`

to a different program (e.g. a COM component/VB) as it
becomes their responsibility.
`CopyToClipboard()`

Places the `CMatrix`

data in the clipboard as CSV text, use this when debugging etc
`WriteAsCSVFile(filename)`

Writes the matrix to a CSV file
`ReadFromCSVFile(const CString& filename)`

Creates a new matrix from a CSV file.
`Dump()`

TRACEs the matrix content to the debug stream
`AssertValid()`

ASSERTs if the object is in an invalid state

#### Transposition

`GetTransposed()`

Returns a new matrix which is a Transpose of the one called on
`Transpose()`

Transposes the current matrix

#### Inversion

`GetInverted()`

Returns the inversion of the current matrix
`Invert()`

Inverts the current matrix

#### Covariant (A' * A)

`Covariant()`

Returns the Covariant of the current matrix

#### Normalisation

`GetNormalised(min, max)`

Returns the matrix with all values scaled between min and max
`Normalise(min, max)`

Normalizes all values in the matrix between min and max

#### Concatenation

`GetConcatinatedColumns(CMatrix)`

Returns a new matrix with the other matrix added onto the right hand side
`ConcatinateColumns(CMatrix)`

Concatenates the additional columns onto the current matrix
`GetConcatenatedRows(CMatrix)`

Returns a new matrix with the other matrix added onto the bottom of the current matrix
`ConcatinateRows(CMatrix)`

Concatenates the additional rows onto the current matrix
`AddColumn(double*)`

Adds a new column onto the current matrix
`AddRow(double*)`

Adds a new row onto the current matrix

#### Extraction/substitution

`ExtractSubMatrix(x, y, x_size, y_size)`

Extract a sub matrix from a larger matrix
`SetSubMatrix(x, y, CMatrix)`

Substitutes a larger matrices elements with those from another matrix
`ExtractDiagonal()`

Returns a x * 1 matrix with the values from the diagonal - square matrices only
`GetSquareMatrix()`

Returns a square matrix of the smaller dimension, by stepping over rows/columns to make the matrix square
`MakeSquare()`

Squares the current matrix by stepping over rows/columns

## Other notes

All the code to handle the allocation/deallocation of matrix data and the reference counting is not covered here in the class interface
as they are all `private`

functions. You can see the documentation in the source code comments. (wow comments....:-D)

If you find any bugs or have some enhancements for the class, I would be happy if you would pass them along, and I will endeavour to keep
the class fully up to date here.

## Updates

### 13th August 2002

- A small problem with
`CMatrixHelper`

when using `operator[][]`

for element read access was fixed by making the return object `const`

.
- An invalid
**ASSERT**ion error in `ExtractSubMatrix`

was fixed.
- The
`operator=`

for `CMatrixHelper`

now copies all member variables across into the target object.

### 2nd July 2002

- A small typo in
`CMatrix::Invert()`

was fixed. Thanks to Jamie Plowman for spotting it.
- As suggested, I made the class
`CMatrixHelper`

constructors `protected`

and made `CMatrix`

a `friend`

so that only `CMatrix`

can construct objects, not a user.

Enjoy!