Translation of the ribbon matrix into the normal

[kalena]

We need to change the ribbons. http://num-anal.srcc.msu.ru/lib_na/org/org_matr.htm (a) The matrices are routine. I don't want to invent a bike. Maybe who knows the libraries/algorithms to make such a transformation?

[emran]

What bike? There's a code for a couple lines.

Here, I put on my knee the transformation into ribbon and back:

using static System.Console;
static void Main ()

{

const int N = 5;

const int KL = 2, KU = 1, B = KL + KU + 1;
var a = new int[N, N] {
    { 11, 12, 00, 00, 00 },
    { 21, 22, 23, 00, 00 },
    { 31, 32, 33, 34, 00 },
    { 00, 42, 43, 44, 45 },
    { 00, 00, 53, 54, 55 }
};

var b = new int[N, B];
for (int i = 0; i < N; i++) {
    for (int j = 0; j < B; j++) {
        int y = i + j - KL;
        b[i, j] = y >= 0 && y < N ? a[i, y] : 0;
    }
}

var c = new int[N, N];
for (int i = 0; i < N; i++) {
    for (int j = 0; j < N; j++) {
        int y = j - i + KL;
        c[i, j] = y >= 0 && y < B ? b[i, y] : 0;
    }
}

Print(a);
Print(b);
Print(c);
ReadKey();

}
static void Print (int[,] m)

{

for (int i = 0; i < m.GetLength(0); i++) {

for (int j = 0; j < m.GetLength(1); j++)

Write("{0:00} ", m[i, j]);

WriteLine();

}

WriteLine();

}

Conclusion:

11 12 00 00 00

21 22 23 00 00

31 32 33 34 00

00 42 43 44 45

00 00 53 54 55

00 00 11 12

00 21 22 23

31 32 33 34

42 43 44 45

53 54 55 00
11 12 00 00 00

21 22 23 00 00

31 32 33 34 00

00 42 43 44 45

00 00 53 54 55

I can't guarantee no bagov. : But on the example of the article, the transformation works, so you're just gonna have to check that everything works right in every case.