# Macreturning matices and pointers to them

#### Quboid

##### macrumors 6502
Original poster
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

##### macrumors 601
simple. you can declare your matrix like this:
Code:
``type Matrix = array [ array [ real ] ]``
let's say you're performing an 8 neighbor relaxation. you can do something like this:
Code:
``````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

##### macrumors 6502
Original poster
simple. you can declare your matrix like this:
Code:
``type Matrix = array [ array [ real ] ]``
let's say you're performing an 8 neighbor relaxation. you can do something like this:
Code:
``````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

##### macrumors 6502
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;

And you can use it like the following

Mat3x3 xyz, becomes a two dim array.