Next: Character Strings in Oct-Files, Previous: Getting Started with Oct-Files, Up: Oct-Files [Contents][Index]

Octave supports a number of different array and matrix classes, the majority of which are based on the Array class. The exception is the sparse matrix types discussed separately below. There are three basic matrix types

`Matrix`

A double precision matrix class defined in

`dMatrix.h`,`ComplexMatrix`

A complex matrix class defined in

`CMatrix.h`, and`BoolMatrix`

A boolean matrix class defined in

`boolMatrix.h`.

These are the basic two-dimensional matrix types of Octave. In addition there are a number of multi-dimensional array types including

`NDArray`

A double precision array class defined in

`dNDArray.h``ComplexNDarray`

A complex array class defined in

`CNDArray.h``boolNDArray`

A boolean array class defined in

`boolNDArray.h``int8NDArray`

`int16NDArray`

`int32NDArray`

`int64NDArray`

8, 16, 32, and 64-bit signed array classes defined in

`int8NDArray.h`,`int16NDArray.h`, etc.`uint8NDArray`

`uint16NDArray`

`uint32NDArray`

`uint64NDArray`

8, 16, 32, and 64-bit unsigned array classes defined in

`uint8NDArray.h`,`uint16NDArray.h`, etc.

There are several basic ways of constructing matrices or
multi-dimensional arrays. Using the class `Matrix`

as an example
one can

- Create an empty matrix or array with the empty constructor. For example:
Matrix a;

This can be used for all matrix and array types.

- Define the dimensions of the matrix or array with a dim_vector which has
the same characteristics as the vector returned from
`size`

. For example:dim_vector dv (2, 3); // 2 rows, 3 columns Matrix a (dv);

This can be used on all matrix and array types.

- Define the number of rows and columns in the matrix. For example:
Matrix a (2, 2)

However, this constructor can only be used with matrix types.

These types all share a number of basic methods and operators. Many bear a resemblance to functions that exist in the interpreter. A selection of useful methods include

- Method:
*T&***operator***() (octave_idx_type)* - Method:
*T&***elem***(octave_idx_type)* The

`()`

operator or`elem`

method allow the values of the matrix or array to be read or set. These can take a single argument, which is of type`octave_idx_type`

, that is the index into the matrix or array. Additionally, the matrix type allows two argument versions of the`()`

operator and elem method, giving the row and column index of the value to obtain or set.

Note that these functions do significant error checking and so in some circumstances the user might prefer to access the data of the array or matrix directly through the fortran_vec method discussed below.

- Method:
**octave_idx_type***numel (void) const* The total number of elements in the matrix or array.

- Method:
*size_t***byte_size***(void) const* The number of bytes used to store the matrix or array.

- Method:
*dim_vector***dims***(void) const* The dimensions of the matrix or array in value of type dim_vector.

- Method:
*int***ndims***(void) const* The number of dimensions of the matrix or array. Matrices are 2-D, but arrays can be N-dimensional.

- Method:
*void***resize***(const dim_vector&)* A method taking either an argument of type

`dim_vector`

, or in the case of a matrix two arguments of type`octave_idx_type`

defining the number of rows and columns in the matrix.

- Method:
*T****fortran_vec***(void)* This method returns a pointer to the underlying data of the matrix or array so that it can be manipulated directly, either within Octave or by an external library.

Operators such an `+`

, `-`

, or `*`

can be used on the
majority of the matrix and array types. In addition there are a number of
methods that are of interest only for matrices such as `transpose`

,
`hermitian`

, `solve`

, etc.

The typical way to extract a matrix or array from the input arguments of
`DEFUN_DLD`

function is as follows

#include <octave/oct.h> DEFUN_DLD (addtwomatrices, args, , "Add A to B") { if (args.length () != 2) print_usage (); NDArray A = args(0).array_value (); NDArray B = args(1).array_value (); return octave_value (A + B); }

To avoid segmentation faults causing Octave to abort this function
explicitly checks that there are sufficient arguments available before
accessing these arguments. It then obtains two multi-dimensional arrays
of type `NDArray`

and adds these together. Note that the array_value
method is called without using the `is_matrix_type`

type. If an
error occurs when attempting to extract the value, Octave will print a
message and throw an exception. The reason to
prefer this is that the arguments might be a type that is not an
`NDArray`

, but it would make sense to convert it to one. The
`array_value`

method allows this conversion to be performed
transparently if possible. If you need to catch errors like this and
perform some kind of cleanup or other operation, you can catch the
`octave_execution_error`

exception.

`A + B`

, operating on two `NDArray`

’s returns an
`NDArray`

, which is cast to an `octave_value`

on the return
from the function. An example of the use of this demonstration function is

addtwomatrices (ones (2, 2), eye (2, 2)) ⇒ 2 1 1 2

A list of the basic `Matrix`

and `Array`

types, the methods to
extract these from an `octave_value`

, and the associated header file is
listed below.

Type | Function | Source Code |
---|---|---|

`RowVector` | `row_vector_value` | dRowVector.h |

`ComplexRowVector` | `complex_row_vector_value` | CRowVector.h |

`ColumnVector` | `column_vector_value` | dColVector.h |

`ComplexColumnVector` | `complex_column_vector_value` | CColVector.h |

`Matrix` | `matrix_value` | dMatrix.h |

`ComplexMatrix` | `complex_matrix_value` | CMatrix.h |

`boolMatrix` | `bool_matrix_value` | boolMatrix.h |

`charMatrix` | `char_matrix_value` | chMatrix.h |

`NDArray` | `array_value` | dNDArray.h |

`ComplexNDArray` | `complex_array_value` | CNDArray.h |

`boolNDArray` | `bool_array_value` | boolNDArray.h |

`charNDArray` | `char_array_value` | charNDArray.h |

`int8NDArray` | `int8_array_value` | int8NDArray.h |

`int16NDArray` | `int16_array_value` | int16NDArray.h |

`int32NDArray` | `int32_array_value` | int32NDArray.h |

`int64NDArray` | `int64_array_value` | int64NDArray.h |

`uint8NDArray` | `uint8_array_value` | uint8NDArray.h |

`uint16NDArray` | `uint16_array_value` | uint16NDArray.h |

`uint32NDArray` | `uint32_array_value` | uint32NDArray.h |

`uint64NDArray` | `uint64_array_value` | uint64NDArray.h |