Some Little Questions

Taklaci Guvercin

I'm in stuck about these questions if you help me i will owe you.

1- Write a program that finds a given sparse matrix is a skew-symmetric matrix or not. The program should print true or false.

Don't take any input from the user, assign the sparse array in the program code.

A skew-symmetric matrix is a square matrix A whose transpose is also its negative; that is, it satisfies the equation A = -A^T. If the entry in the i ^th row and j ^th column is a_ij, i.e. A = (a_ij) then the symmetric condition becomes a_ij = -a_ji.

2- Write a program that shifts the elements of each row of a sparse matrix array by n positions.

Example:

Input:

int[,] s = new int[,] {{6,6,8},{0,0,15},{0,3,22},{0,5,-15},{1,1,11}, {1,2,3}, {2,3,-6}, {4,0,91}, {5,2,28}};

15 0 0 22 0 -15

0 11 3 0 0 0

0 0 0 -6 0 0

0 0 0 0 0 0

91 0 0 0 0 0

0 0 28 0 0 0

Shift by 2 positions

Output:

0 -15 15 0 0 22

0 0 0 11 3 0

0 0 0 0 0 -6

0 0 0 0 0 0

0 0 91 0 0 0

0 0 0 0 28 0

4 Replies

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Vulpes15y ago
Accepted answer
It looks to me as though the values in each row of the matrix are being rotated by 'n' positions, which could be done right (positive 'n') or left (negative 'n').

I don't see what difference it makes that the matrix is sparse as the code is just the same as for a 'dense' matrix. Sure, you could put in code to check that you're not moving a zero element into a place which already had a zero element but it hardly seems worth the effort.

Anyway this should work for any matrix:

using System;

class Program
{
static void Main()
{

int[,] s = new int[,]
{
{ 15, 0, 0, 22, 0, -15 },
{ 0, 11, 3, 0, 0, 0 },
{ 0, 0, 0, -6, 0, 0 },
{ 0, 0, 0, 0, 0, 0 },
{ 91, 0, 0, 0, 0, 0 },
{ 0, 0, 28, 0, 0, 0 }
};

Console.WriteLine("Original Matrix is\n");
PrintMatrix(s);

RotateMatrixRows(s, 2);
Console.WriteLine("\nShifted Matrix is\n");
PrintMatrix(s);
Console.ReadKey();
}

static void RotateMatrixRows(int[,] matrix, int numElements)
{
if (matrix == null) return;
int m = matrix.GetLength(0);
int n = matrix.GetLength(1);
if (m == 0 || n == 0) return;

numElements = numElements % n;

if (numElements == 0) return;

if (numElements > 0)
{
for(int i = 0; i < numElements; i++)
{
for(int j = 0; j < m; j++)
{
int lastCol = matrix[j, n-1];
for(int k = n - 2; k >= 0; k--) matrix[j, k + 1] = matrix[j, k];
matrix[j, 0] = lastCol;
}
}
}
else
{
numElements = -numElements;
for(int i = 0; i < numElements; i++)
{
for(int j = 0; j < m; j++)
{
int firstCol = matrix[j, 0];
for(int k = 1; k < n; k++) matrix[j, k - 1] = matrix[j, k];
matrix[j, n - 1] = firstCol;
}
}
}
}

static void PrintMatrix(int[,] matrix)
{

for(int a = 0; a < matrix.GetLength(0); a++)
{
for (int b = 0; b < matrix.GetLength(1); b++)
{
Console.Write("{0,3} ", matrix[a, b]);
}
Console.WriteLine();
}
}
}
Sam Hobbs15y ago
I know very little about sparse matrices, but isn't that a dense matrix in that program?

Also, I don't understand the problem of shifting the "elements of each row of a sparse matrix array by n position". I don't understand how the result corresponds with the input. So I cannot help with that; I hope someone can. Unfortunately it is too late for Vulpes to get to this before Monday morning.

Your program says "Given Matrix is : " but I think it does not show the given matrix. Since the matrix is a typical dense matrix, I could help with that but I assume that does not help.
Taklaci Guvercin15y ago
Well,I tried and solved other question but i'm still getting stuck in question 2.

static void Main(string[] args)
Console.WriteLine("Given Matrix is : ");

int[,] s = new int[,] { { 15, 0, 0, 22, 0, -15 }, { 0, 11, 3, 0, 0, 0 }, { 0, 0, 0, -6, 0, 0 }, { 0, 0, 0, 0, 0, 0 }, { 91,0, 0, 0, 0, 0 }, { 0, 0, 28, 0, 0, 0 } };
for(int a = 0; a <= 5; a++)
for (int b = 0; b <= 5; b++)
{

Console.Write(" ", +s[a, b]);
Console.WriteLine();
Console.WriteLine("Shiftted Matrix is : ");
int[,] x = new int[,] { { 0,-15,15,0, 0, 22 }, { 0, 0 , 0 ,11 ,3 , 0 }, { 0, 0 ,0, 0, 0,-6 }, { 0, 0, 0, 0, 0, 0 }, {0, 0,91,0 ,0 , 0 }, {0,0,0,0,28, 0 } };
for (int i = 0; i <= 5; i++)
for (int j = 0; j <= 5; j++)
{

Console.Write(" ", +s[i, j]);
Console.WriteLine();
}

{

}

Console.Read();
Sam Hobbs15y ago
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