[Shape-univ] octave: hadamard product = entrywise product = Schur product

[Boud Roukema]

hi again SR/GR students

In octave, if you define matrices and column vectors and "row one-forms"
(called row vectors in octave), then operations you might find useful
include:

1. 
http://en.wikipedia.org/wiki/Matrix_multiplication#Hadamard_product
Hadamard product = entrywise product = Schur product

4-element column vectors  A and B

A .* B   gives you the Hadamard product = entrywise product = Schur product
meaning another 4-element column vector

(Hadamard product also has a different meaning - see the Wikipedia section)

- similar for  row vectors, matrices, etc.


2.  sum(A)

For a 1D column vector or "row one-form", the meaning and syntax are obvious.

For a 2D matrix, you can add along rows or columns - but you probably don't 
need this for these tensor exercises.


3. work on or print a row or column of a matrix

example: the 2nd column of matrix  g   is

g(:,2)

example: the 3rd row of matrix  g   is

g(3,:)



4. get the inverse of matrix   g

type

doc inverse

and read the documentation :).


pozdr
boud



On Thu, 9 Jun 2011, Boud Roukema wrote:

> hi SR/GR students,
>
> Most of you are at KRA now, so i've opened up scoring for
> the exercises until 15.30.  For people who cannot finish the
> exercises today, please propose another day e.g. next week.
> There is no point doing the exam if you have not passed
> (got at least 3 points) in the zaliczenia (there's probably
> also a formal UMK rule on this...)
>
> For the exam, some people are thinking of
>
>  Tuesday 21.06.2011, from the 9.00 bus
>
> but this is only a proposal, not yet definite.
>
> pozdr
> boud
>
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