Unexpected Diamond square Algorithm results - c#

I'm currently trying to implement the Diamond Square algorithm and while the thing is somewhat working, I'm confused by the HeightMap.
Here it is :
As you can see the squares are clearly outlined by brighters values, while the losanges are outlined by darker values.
I really cant understand why. I know that the size of the map is really small but I don't think that's the expected result anyway, and I got the same behavior with larger sizes.
Here's my code :
public class TerrainBuilder
{
private Terrain Terrain = null;
private Random r = new Random();
private int espace;
public void Init(Terrain _terrain)
{
Terrain = _terrain;
espace = Terrain.SIZE - 1;
}
public void DiamondAlgoritm()
{
if (Terrain == null)
return;
//Initialization
Terrain.HeightMap[0, 0] = r.Next() % 255;
Terrain.HeightMap[0, Terrain.SIZE - 1] = r.Next() % 255;
Terrain.HeightMap[Terrain.SIZE - 1, 0] = r.Next() % 255;
Terrain.HeightMap[Terrain.SIZE - 1, Terrain.SIZE - 1] = r.Next() % 255;
//randominess
int decalage = 128;
while (espace > 1)
{
int demiSpace = espace / 2;
//diamond phase
for (int i = demiSpace; i < espace; i = i + espace)
{
for (int j = demiSpace; j < espace; j = j + espace)
{
var avg = Terrain.HeightMap[i + demiSpace, j + demiSpace] + Terrain.HeightMap[i + demiSpace, j - demiSpace] + Terrain.HeightMap[i - demiSpace, j + demiSpace] + Terrain.HeightMap[i - demiSpace, j - demiSpace];
avg /= 4;
Terrain.HeightMap[i, j] = Normalize(avg + r.Next() % decalage);
}
}
//carre phase
for (int i = 0; i < Terrain.SIZE; i += demiSpace)
{
int delay = 0;
if (i % espace == 0)
delay = demiSpace;
for (int j = delay; j < Terrain.SIZE; j += espace)
{
double somme = 0;
int n = 0;
if (i >= demiSpace)
somme = somme + Terrain.HeightMap[i - demiSpace, j];
n = n + 1;
if (i + demiSpace < Terrain.SIZE)
somme = somme + Terrain.HeightMap[i + demiSpace, j];
n = n + 1;
if (j >= demiSpace)
somme = somme + Terrain.HeightMap[i, j - demiSpace];
n = n + 1;
if (j + demiSpace < Terrain.SIZE)
somme = somme + Terrain.HeightMap[i, j + demiSpace];
n = n + 1;
Terrain.HeightMap[i, j] = Normalize(somme / n + r.Next() % decalage);
}
}
espace = demiSpace;
}
}
private double Normalize(double value)
{
return Math.Max(Math.Min(value, 255), 0);
}
}
I would like some help to understand this problem.


During the diamond phase, you don't iterate over the whole map. You only calculate the first square (equal to espace).
Change your loop termination conditions like this:
for (int i = demiSpace; i < Terrain.SIZE; i = i + espace)
{
for (int j = demiSpace; j < Terrain.SIZE; j = j + espace)
{
var avg = Terrain.HeightMap[i + demiSpace, j + demiSpace] +
Terrain.HeightMap[i + demiSpace, j - demiSpace] +
Terrain.HeightMap[i - demiSpace, j + demiSpace] +
Terrain.HeightMap[i - demiSpace, j - demiSpace];
avg /= 4;
Terrain.HeightMap[i, j] = Normalize(avg + r.Next() % decalage);
}
}
Also, you never adjust your randomness variable (decalage), which should get smaller as you reduce the size of espace.

Related

Can't perambulate indexes in matrix the right way

Hello. I have this task to sum the numbers as shown. Tried everything I can, but still not the right answer. Can I have some guidance?
static void Main(string[] args)
{
string input = Console.ReadLine();
int n = (int)char.GetNumericValue(input[0]);
int m = (int)char.GetNumericValue(input[2]);
int[,] matrix = new int[n, m];
int sum = 0;
//fill matrix
for (int i = 0; i < n; i++)
{
for (int j = 0; j < m; j++)
{
matrix[i, j] = (j * 3 + 1) + i * 3;
}
}
for (int i = 0; i < matrix.GetLength(0) - 1; i+=1)
{
for (int j = 0; j < matrix.GetLength(1) - i; j+=1)
{
if (i % 2 == 0)
{
sum += matrix[i, j + i] + matrix[i + 1, j + 1];
}
}
}
Console.WriteLine(sum);
}

I think you would've a easier time hard coding the input (and naming them as "columns" and "rows" instead, much more readable).
What is the expected output? Not sure I'm following this sum. I'm guessing, 297? If so:
for (int i = 0; i < matrix.GetLength(0); i++)
{
for (int j = 0; j < matrix.GetLength(1); j++)
{
Console.Write(matrix[i, j] + " ");
if(j == 5) Console.WriteLine();
if (matrix[i, j] % 2 != 0)
{
if (i == 0 || i == matrix.GetLength(0) - 1
|| j == 0 || j == matrix.GetLength(0))
{
sum += (matrix[i, j]);
}
else
{
sum += (matrix[i, j] * 2);
}
}
}
}

Why Am I Getting The Incorrect Levenshtein Distance?

I am attempting to implement the Levenshtein Distance algorithm in C# (for practice and because it'd be handy to have). I used an implementation from the Wikipedia page but for some reason I'm getting the wrong distance on one set of words. Here's the code (from LinqPad):
void Main()
{
var ld = new LevenshteinDistance();
int dist = ld.LevenshteinDistanceCalc("sitting","kitten");
dist.Dump();
}
// Define other methods and classes here
public class LevenshteinDistance
{
private int[,] distance;
public int LevenshteinDistanceCalc(string source, string target)
{
int sourceSize = source.Length, targetSize = target.Length;
distance = new int[sourceSize, targetSize];
for (int sIndex = 0; sIndex < sourceSize; sIndex++)
{
distance[sIndex, 0] = sIndex;
}
for (int tIndex = 0; tIndex < targetSize; tIndex++)
{
distance[0,tIndex] = tIndex;
}
// for j from 1 to n:
// for i from 1 to m:
// if s[i] = t[j]:
// substitutionCost:= 0
// else:
// substitutionCost:= 1
// d[i, j] := minimum(d[i - 1, j] + 1, // deletion
// d[i, j - 1] + 1, // insertion
// d[i - 1, j - 1] + substitutionCost) // substitution
//
//
// return d[m, n]
for (int tIndex = 1; tIndex < targetSize; tIndex++)
{
for (int sIndex = 1; sIndex < sourceSize; sIndex++)
{
int substitutionCost = source[sIndex] == target[tIndex] ? 0 : 1;
int deletion = distance[sIndex-1, tIndex]+1;
int insertion = distance[sIndex,tIndex-1]+1;
int substitution = distance[sIndex-1, tIndex-1] + substitutionCost;
distance[sIndex, tIndex] = leastOfThree(deletion, insertion, substitution);
}
}
return distance[sourceSize-1,targetSize-1];
}
private int leastOfThree(int a, int b, int c)
{
return Math.Min(a,(Math.Min(b,c)));
}
}
When I try "sitting" and "kitten" I get an LD of 2 (should be 3). Yet when I try "Saturday" and "Sunday" I get an LD of 3 (which is correct). I know something's wrong but I can't figure out what I'm missing.

The example on wikipedia uses 1-based strings. In C# we use 0-based strings.
In their matrix the 0-row and 0-column does exist. So the size of their matrix is [source.Length + 1, source.Length + 1] In your code it doesn't exist.
public int LevenshteinDistanceCalc(string source, string target)
{
int sourceSize = source.Length, targetSize = target.Length;
distance = new int[sourceSize + 1, targetSize + 1];
for (int sIndex = 1; sIndex <= sourceSize; sIndex++)
distance[sIndex, 0] = sIndex;
for (int tIndex = 1; tIndex <= targetSize; tIndex++)
distance[0, tIndex] = tIndex;
for (int tIndex = 1; tIndex <= targetSize; tIndex++)
{
for (int sIndex = 1; sIndex <= sourceSize; sIndex++)
{
int substitutionCost = source[sIndex-1] == target[tIndex-1] ? 0 : 1;
int deletion = distance[sIndex - 1, tIndex] + 1;
int insertion = distance[sIndex, tIndex - 1] + 1;
int substitution = distance[sIndex - 1, tIndex - 1] + substitutionCost;
distance[sIndex, tIndex] = leastOfThree(deletion, insertion, substitution);
}
}
return distance[sourceSize, targetSize];
}

Your matrix isn't big enough.
In the pseudo-code, s and t have lengths m and n respectively (char s[1..m], char t[1..n]). The matrix however has dimentions [0..m, 0..n] - i.e. one more than the length of the strings in each direction. You can see this in the tables below the pseudo-code.
So the matrix for "sitting" and "kitten" is 7x8, but your matrix is only 6x7.
You're also indexing into the strings incorrectly, because the strings in the pseudo-code are 1-indexed, but C#'s strings are 0-indexed.
After fixing these, you get this code, which works with "sitting" and "kitten":
public static class LevenshteinDistance
{
public static int LevenshteinDistanceCalc(string source, string target)
{
int sourceSize = source.Length + 1, targetSize = target.Length + 1;
int[,] distance = new int[sourceSize, targetSize];
for (int sIndex = 0; sIndex < sourceSize; sIndex++)
{
distance[sIndex, 0] = sIndex;
}
for (int tIndex = 0; tIndex < targetSize; tIndex++)
{
distance[0, tIndex] = tIndex;
}
// for j from 1 to n:
// for i from 1 to m:
// if s[i] = t[j]:
// substitutionCost:= 0
// else:
// substitutionCost:= 1
// d[i, j] := minimum(d[i - 1, j] + 1, // deletion
// d[i, j - 1] + 1, // insertion
// d[i - 1, j - 1] + substitutionCost) // substitution
//
//
// return d[m, n]
for (int tIndex = 1; tIndex < targetSize; tIndex++)
{
for (int sIndex = 1; sIndex < sourceSize; sIndex++)
{
int substitutionCost = source[sIndex - 1] == target[tIndex - 1] ? 0 : 1;
int deletion = distance[sIndex - 1, tIndex] + 1;
int insertion = distance[sIndex, tIndex - 1] + 1;
int substitution = distance[sIndex - 1, tIndex - 1] + substitutionCost;
distance[sIndex, tIndex] = leastOfThree(deletion, insertion, substitution);
}
}
return distance[sourceSize - 1, targetSize - 1];
}
private static int leastOfThree(int a, int b, int c)
{
return Math.Min(a, (Math.Min(b, c)));
}
}
(I also took the liberty of making distance a local variable since there's no need for it to be a field (it only makes your class non-threadsafe), and also making it static to avoid the unnecessary instantiation).
To debug this, I put a breakpoint on return distance[sourceSize - 1, targetSize - 1] and compared distance to the table on Wikipedia. It was very obvious that it was too small.

2d array challenge access elements

Attempting the hackerRank Q from https://www.hackerrank.com/challenges/2d-array
static void Main(String[] args)
{
int[][] arr = new int[6][];
for (int arr_i = 0; arr_i < 6; arr_i++)
{
string[] arr_temp = Console.ReadLine().Split(' ');
arr[arr_i] = Array.ConvertAll(arr_temp, Int32.Parse);
}
int[] sum = new int[6];
List<int> n = new List<int>();
for (int i = 0; i + 2 < arr.Length; i++)
{
for (int j = 0; j + 2 < arr.GetLength(0); j++)
{
sum[j] = arr[i][j] + arr[i][j + 1] + arr[i][j + 2] +
arr[i + 1][j + 1] +
arr[i + 2][j] + arr[i + 2][j + 1] + arr[i + 2][j + 2];
n.Add(sum[j]);
}
}
Console.WriteLine(n.Max());
}
}
}
If I run this program and enter the following as contents of 'arr'
111111
222222
333333
444444
555555
666666
Here I am trying to add 1 + 1 + 1
+ 2 +
3 + 3 + 3
using sum[j] = arr[i][j] + arr[i][j + 1] + arr[i][j + 2] +
arr[i + 1][j + 1] +
arr[i + 2][j] + arr[i + 2][j + 1] + arr[i + 2][j + 2];
but arr[i][j] returns 111111
how can I access 1? is this the right answer to the question on hackerrank?

Hope below code helps you
public class Solution {
private static final int _MAX = 6; // size of matrix
private static final int _OFFSET = 2; // hourglass width
private static int matrix[][] = new int[_MAX][_MAX];
private static int maxHourglass = -63; // initialize to lowest possible sum (-9 x 7)
/** Given a starting index for an hourglass, sets maxHourglass
* #param i row
* #param j column
**/
private static void hourglass(int i, int j){
int tmp = 0; // current hourglass sum
// sum top 3 and bottom 3 elements
for(int k = j; k <= j + _OFFSET; k++){
tmp += matrix[i][k];
tmp += matrix[i + _OFFSET][k];
}
// sum middle element
tmp += matrix[i + 1][j + 1];
if(maxHourglass < tmp){
maxHourglass = tmp;
}
}
public static void main(String[] args) {
// read inputs
Scanner scan = new Scanner(System.in);
for(int i=0; i < _MAX; i++){
for(int j=0; j < _MAX; j++){
matrix[i][j] = scan.nextInt();
}
}
scan.close();
// find maximum hourglass
for(int i=0; i < _MAX - _OFFSET; i++){
for(int j=0; j < _MAX - _OFFSET; j++){
hourglass(i, j);
}
}
// print maximum hourglass
System.out.println(maxHourglass);
}
}

add wavelet filters to discrete Haar wavelet transform (DWT)

I need help for 1-level 5/3 discrete Haar wavelet transform (DWT) source code with c# .
I use this project, and the methods of forward wavelet transform is here :
FWT(double[] data)
{
int h = data.Length >> 1;
for (int i = 0; i < h; i++)
{
int k = (i << 1);
temp[i] = data[k] * s0 + data[k + 1] * s1;
temp[i + h] = data[k] * w0 + data[k + 1] * w1;
}
}
FWT(double[,] data)
{
for (int k = 0; k < 1; k++)
{
for (int i = 0; i < rows / (k+1); i++)
{
for (int j = 0; j < row.Length / (k+1); j++)
row[j] = data[i, j];
FWT(row);
for (int j = 0; j < row.Length / (k+1); j++)
data[i, j] = row[j];
}
for (int j = 0; j < cols / (k+1); j++)
{
for (int i = 0; i < col.Length / (k+1); i++)
col[i] = data[i, j];
FWT(col);
for (int i = 0; i < col.Length / (k+1); i++)
data[i, j] = col[i];
}
}
}
w0 = 0.5; w1 = -0.5;s0 = 0.5;s1 = 0.5;
I searched about this topic in the papers , but I don't understand the algorithm of 5/3 or 9/7 wavelet filters and how can I change this code?
Any help would be much appreciated

You may find it useful: implementation of jpeg2000 decoder in pdf.js.
The implementation of the core of the 5-3 code:
function reversibleTransformFilter(x, offset, length) {
var len = length >> 1;
offset = offset | 0;
var j, n;
for (j = offset, n = len + 1; n--; j += 2) {
x[j] -= (x[j - 1] + x[j + 1] + 2) >> 2;
}
for (j = offset + 1, n = len; n--; j += 2) {
x[j] += (x[j - 1] + x[j + 1]) >> 1;
}
};

Levenshtein distance c# count error type

I found this bit of code that computes Levenshtein's distance between an answer and a guess:
int CheckErrors(string Answer, string Guess)
{
int[,] d = new int[Answer.Length + 1, Guess.Length + 1];
for (int i = 0; i <= Answer.Length; i++)
d[i, 0] = i;
for (int j = 0; j <= Guess.Length; j++)
d[0, j] = j;
for (int j = 1; j <= Guess.Length; j++)
for (int i = 1; i <= Answer.Length; i++)
if (Answer[i - 1] == Guess[j - 1])
d[i, j] = d[i - 1, j - 1]; //no operation
else
d[i, j] = Math.Min(Math.Min(
d[i - 1, j] + 1, //a deletion
d[i, j - 1] + 1), //an insertion
d[i - 1, j - 1] + 1 //a substitution
);
return d[Answer.Length, Guess.Length];
}
But I need a way to do a count for the amount of times each error occurs. Is there an easy way to implement that?

Seems like you could add counters for each of the operations:
if (Answer[i - 1] == Guess[j - 1])
d[i, j] = d[i - 1, j - 1]; //no operation
else
{
int del = d[i-1, j] + 1;
int ins = d[i, j-1] + 1;
int sub = d[i-1, j-1] + 1;
int op = Math.Min(Math.Min(del, ins), sub);
d[i, j] = op;
if (i == j)
{
if (op == del)
++deletions;
else if (op == ins)
++insertions;
else
++substitutions;
}
}

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