Tips and tricks
C++
Real matrix operations
This is a table of matrix operations commonly performed in Octave and their equivalents in C++ when using the octave libraries.
| Operation | Octave | C++ |
| add | A+B | A+B |
| subtract | A-B | A-B |
| matrix multiplication | A*B | A*B |
| element multiplication | A.*B | product(A,B) |
| element division | A./B | quotient(A,B) |
| transpose* | A' | A.transpose() |
| select element m,n of A** | A(m,n) | A(m-1,n-1) |
| select row N of A** | A(N,:) | A.row(N-1) |
| select column N of A** | A(:,N) | A.column(N-1) |
| extract submatrix of A | A(a:b,c:d) | A.extract(a-1,c-1,b-1,d-1) |
| absolute value of A | abs(A) | A.abs() |
| comparison to scalar*** | A>2 | mx_el_gt(A,2) |
A<2 | mx_el_lt(A,2) | |
A==2 | mx_el_eq(A,2) | |
A~=2 | mx_el_ne(A,2) | |
A>=2 | mx_el_ge(A,2) | |
A<=2 | mx_el_le(A,2) | |
| matrix of zeros | A=zeros(m,n) | A.fill(0.0) |
| matrix of ones | A=ones(m,n) | A.fill(1.0) |
| identity matrix | eye(N) | identity_matrix(N,N) |
| inverse of A | inv(A) | A.inverse() |
| pseudoinverse of A | pinv(A) | A.pseudo_inverse() |
| diagonal elements of A | diag(A) | A.diag() |
| column vector | A(:) | ColumnVector(A.reshape (dim_vector(A.length()))) |
| row vector | A(:)' | RowVector(A.reshape (dim_vector(A.length()))) |
| check for Inf or <a href="wiki.pl?NaN">NaN</a> | any(~isfinite(A)) | A.any_element_is_inf_or_nan() |
| stack two matrices vertically | A=[B;C] | B.stack(C) |
| uniform random matrix | rand(a,b) | octave_rand::distribution("uniform"); octave_rand::matrix(a,b) |
| normal random matrix | randn(a,b) | octave_rand::distribution("normal"); octave_rand::matrix(a,b) |
| sum squares of columns | sumsq(A) | A.sumsq() |
| sum along columns | sum(A,1) | A.sum(0) |
| sum along rows | sum(A,2) | A.sum(1) |
| product along columns | prod(A,1) | A.prod(0) |
| product along rows | prod(A,2) | A.prod(1) |
| cumsum along columns | cumsum(A,1) | A.cumsum(0) |
| cumsum along rows | cumsum(A,2) | A.cumsum(1) |
| cumproduct along columns | cumprod(A,1) | A.cumprod(0) |
| cumproduct along rows | cumprod(A,2) | A.cumprod(1) |
| number of rows | size(A,1) | A.rows() |
| number of columns | size(A,2) | A.cols() |
Notes: *Transpose, addition, and multiplication operations also apply to RowVector, ComplexRowVector, ColumnVector, and ComplexColumnVector data types when the dimensions are in agreement. **The difference is due to the fact that arrays are zero-based in C++, but one-based in Octave. ***The names of Octave internal functions, such as mx_el_gt, are not documented and are subject to change. Functions such as mx_el_gt may eventually be available at both the scripting level and in C++ under more common names such as gt.
Complex Matrix Operations
| Operation | Octave | C++ |
| conjugate tranpose | A' | A.hermitian() |