﻿ row or column major

# row or column major

They could be row-major matrices stored in row order, or column-major matrices stored in column order. It may be more obvious if you look at how a vector is treated when multiplied with an appropriate matrix. Arrays are just arrays (and hopefully sequential in memory). If you implement a matrix as an array of arrays, it can be either row or column major, depending on whether you define the first index to be a row or a column index. That being said, theres no real reason we cant re-interpret Smiths algorithm in row-major form (he didnt write it in either direction) and theres a moderately good chance it will be tricky to program regardless of the choice between row-major and column-major. Definition of row/column vectors. For coherence and to make things easier to understand there are two ways to write vectors. We can write them horizontally ( row vector) or vertically (column vector). Row vector RV. Column vector CV. When working with vectors, this is purely aesthetic. In column-major order, for any number of rows, fewer columns lays out narrower. Thats not necessarily true for row-major order. e.g. for 7 items on two lines, in column-major order the choices are Wether to call this layout row major or column major depends on your view of the vectors you are going to transform. Imagining them to be column vectors and thus post multiplied you will have the scenario below dolfin::parameters["linearalgebrabackend"] "uBLAS" dolfin::Matrix A boost::tuples::tuple t t A.data () How can I know if the matrix is stored with a row major or a column major orientation? But that doesnt say whether its row-major or column-major.

Is every 4 elements a column of the matrix or a row?See, all column-major and row-major do is define how a matrix is encoded as an array of floats. Row-major vs. column-major is just a storage order thing and doesnt have anything to do with what kind of vectors you use.Another myth is that matrix multiplication order depends on whether youre using row-major or column-major. EX languages: C, C, Python Column Major: Values are stored in column wise. EX Platforms: MATLAB, Fortran, OpenGL Row Major a[3][3] 10 20 30BaseAddress (i Rowsize Colsize j Colsize K) size Column Major Column Major Address Calculation: One Dimension Array a[i] In computing, row-major order and column-major order are methods for storing multidimensional arrays in linear storage such as random access memory. The difference between the orders lies in which elements of an array are contiguous in memory. It is common sense that FORTRAN store array in column-major order. But many functions, libraries treat array in row-major order. For example, in ifort document for matmul This little slice thing however, has everything one would need to access a row-major-storage column-wise or a column-major-storage row-wise - it has a start, a length, and a stride - the latter represents the "distance to next bucket" I mentioned. The terms row-major and column-major stem from the terminology related to grouping objects.