View Full Version : returning matices and pointers to them

Quboid

Sep 2, 2007, 09:58 PM

hey all,

I am doing some homework here (for tomorrow) and the last few programs seem a bit tricky. I have the logic for the one i am doing now down already, however, it would require me returning a matrix from my function. I am not to keen on trying to return a matrix, instead i am looking at return a pointer to matrix created.

how do i declare the function in this case?, and how do i declare the matrix in question?

thanks a million

zimv20

Sep 2, 2007, 10:15 PM

simple. you can declare your matrix like this:

type Matrix = array [ array [ real ] ]

let's say you're performing an 8 neighbor relaxation. you can do something like this:

function relax ( a : Matrix returns Matrix )

for row in a at i cross elt in row at j

avg := (elt a[i, j-1] a[i, j 1]

a[i 1, j-1] a[i 1, j] a[i 1, j 1]

a[i-1, j-1] a[i-1, j] a[i-1, j 1]) / 9.0

returns array of avg

end for

end function

so just specify your return type as Matrix, and return it when done.

Quboid

Sep 2, 2007, 10:21 PM

simple. you can declare your matrix like this:

type Matrix = array [ array [ real ] ]

let's say you're performing an 8 neighbor relaxation. you can do something like this:

function relax ( a : Matrix returns Matrix )

for row in a at i cross elt in row at j

avg := (elt a[i, j-1] a[i, j 1]

a[i 1, j-1] a[i 1, j] a[i 1, j 1]

a[i-1, j-1] a[i-1, j] a[i-1, j 1]) / 9.0

returns array of avg

end for

end function

so just specify your return type as Matrix, and return it when done.

I'm sorry i forgot to specify that i am programming in c++.

garethlewis2

Sep 3, 2007, 03:38 AM

Steps for you to do.

Declare your function line the following.

Mat3x3 blahFunction(something *) {

// Mat3x3 can be a class, structure or for C a two-dim array

if a class, use a new operator.

if doing it like C, use malloc. and cast the malloced memory to the type

Mat3x3.

// Do the operations on the matrix.

// return the Mat3x3

return mat3x3;

}

At the top of your file, if a 3x3 array use the following.

typedef double Mat3x3[3][3];

And you can use it like the following

Mat3x3 xyz, becomes a two dim array.