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# Double[,], inversion C#

By : Alex Vohs
Date : November 19 2020, 03:01 PM
hop of those help? Here you have a working example, just copy the entire code into a console project and run it. I took it from this link https://jamesmccaffrey.wordpress.com/2015/03/06/inverting-a-matrix-using-c/
code :
`````` using System;
using System.Collections.Generic;
using System.Linq;

namespace matrixExample
{

class Program
{

static void Main(string[] args)
{

double[][] m = new double[][] { new double[] { 7, 2, 1 }, new double[] { 0, 3, -1 }, new double[] { -3, 4, 2 } };
double[][] inv = MatrixInverse(m);

//printing the inverse
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < 3; j++)
Console.Write(Math.Round(inv[i][j], 1).ToString().PadLeft(5, ' ') + "|");
Console.WriteLine();
}

}

static double[][] MatrixCreate(int rows, int cols)
{
double[][] result = new double[rows][];
for (int i = 0; i < rows; ++i)
result[i] = new double[cols];
return result;
}

static double[][] MatrixIdentity(int n)
{
// return an n x n Identity matrix
double[][] result = MatrixCreate(n, n);
for (int i = 0; i < n; ++i)
result[i][i] = 1.0;

return result;
}

static double[][] MatrixProduct(double[][] matrixA, double[][] matrixB)
{
int aRows = matrixA.Length; int aCols = matrixA[0].Length;
int bRows = matrixB.Length; int bCols = matrixB[0].Length;
if (aCols != bRows)
throw new Exception("Non-conformable matrices in MatrixProduct");

double[][] result = MatrixCreate(aRows, bCols);

for (int i = 0; i < aRows; ++i) // each row of A
for (int j = 0; j < bCols; ++j) // each col of B
for (int k = 0; k < aCols; ++k) // could use k less-than bRows
result[i][j] += matrixA[i][k] * matrixB[k][j];

return result;
}

static double[][] MatrixInverse(double[][] matrix)
{
int n = matrix.Length;
double[][] result = MatrixDuplicate(matrix);

int[] perm;
int toggle;
double[][] lum = MatrixDecompose(matrix, out perm,
out toggle);
if (lum == null)
throw new Exception("Unable to compute inverse");

double[] b = new double[n];
for (int i = 0; i < n; ++i)
{
for (int j = 0; j < n; ++j)
{
if (i == perm[j])
b[j] = 1.0;
else
b[j] = 0.0;
}

double[] x = HelperSolve(lum, b);

for (int j = 0; j < n; ++j)
result[j][i] = x[j];
}
return result;
}

static double[][] MatrixDuplicate(double[][] matrix)
{
// allocates/creates a duplicate of a matrix.
double[][] result = MatrixCreate(matrix.Length, matrix[0].Length);
for (int i = 0; i < matrix.Length; ++i) // copy the values
for (int j = 0; j < matrix[i].Length; ++j)
result[i][j] = matrix[i][j];
return result;
}

static double[] HelperSolve(double[][] luMatrix, double[] b)
{
// before calling this helper, permute b using the perm array
// from MatrixDecompose that generated luMatrix
int n = luMatrix.Length;
double[] x = new double[n];
b.CopyTo(x, 0);

for (int i = 1; i < n; ++i)
{
double sum = x[i];
for (int j = 0; j < i; ++j)
sum -= luMatrix[i][j] * x[j];
x[i] = sum;
}

x[n - 1] /= luMatrix[n - 1][n - 1];
for (int i = n - 2; i >= 0; --i)
{
double sum = x[i];
for (int j = i + 1; j < n; ++j)
sum -= luMatrix[i][j] * x[j];
x[i] = sum / luMatrix[i][i];
}

return x;
}

static double[][] MatrixDecompose(double[][] matrix, out int[] perm, out int toggle)
{
// Doolittle LUP decomposition with partial pivoting.
// rerturns: result is L (with 1s on diagonal) and U;
// perm holds row permutations; toggle is +1 or -1 (even or odd)
int rows = matrix.Length;
int cols = matrix[0].Length; // assume square
if (rows != cols)
throw new Exception("Attempt to decompose a non-square m");

int n = rows; // convenience

double[][] result = MatrixDuplicate(matrix);

perm = new int[n]; // set up row permutation result
for (int i = 0; i < n; ++i) { perm[i] = i; }

toggle = 1; // toggle tracks row swaps.
// +1 -greater-than even, -1 -greater-than odd. used by MatrixDeterminant

for (int j = 0; j < n - 1; ++j) // each column
{
double colMax = Math.Abs(result[j][j]); // find largest val in col
int pRow = j;
//for (int i = j + 1; i less-than n; ++i)
//{
//  if (result[i][j] greater-than colMax)
//  {
//    colMax = result[i][j];
//    pRow = i;
//  }
//}

// reader Matt V needed this:
for (int i = j + 1; i < n; ++i)
{
if (Math.Abs(result[i][j]) > colMax)
{
colMax = Math.Abs(result[i][j]);
pRow = i;
}
}
// Not sure if this approach is needed always, or not.

if (pRow != j) // if largest value not on pivot, swap rows
{
double[] rowPtr = result[pRow];
result[pRow] = result[j];
result[j] = rowPtr;

int tmp = perm[pRow]; // and swap perm info
perm[pRow] = perm[j];
perm[j] = tmp;

toggle = -toggle; // adjust the row-swap toggle
}

// --------------------------------------------------
// This part added later (not in original)
// and replaces the 'return null' below.
// if there is a 0 on the diagonal, find a good row
// from i = j+1 down that doesn't have
// a 0 in column j, and swap that good row with row j
// --------------------------------------------------

if (result[j][j] == 0.0)
{
// find a good row to swap
int goodRow = -1;
for (int row = j + 1; row < n; ++row)
{
if (result[row][j] != 0.0)
goodRow = row;
}

if (goodRow == -1)
throw new Exception("Cannot use Doolittle's method");

// swap rows so 0.0 no longer on diagonal
double[] rowPtr = result[goodRow];
result[goodRow] = result[j];
result[j] = rowPtr;

int tmp = perm[goodRow]; // and swap perm info
perm[goodRow] = perm[j];
perm[j] = tmp;

toggle = -toggle; // adjust the row-swap toggle
}
// --------------------------------------------------
// if diagonal after swap is zero . .
//if (Math.Abs(result[j][j]) less-than 1.0E-20)
//  return null; // consider a throw

for (int i = j + 1; i < n; ++i)
{
result[i][j] /= result[j][j];
for (int k = j + 1; k < n; ++k)
{
result[i][k] -= result[i][j] * result[j][k];
}
}

} // main j column loop

return result;
}

}
}
``````

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## Events in an Inversion of Control (Dependency Inversion) system go which way?

By : Ahmer Jamil
Date : March 29 2020, 07:55 AM
With these it helps For the sake of brevity, I'm going to refer to the objects contained within the container as "client objects" or just "clients"...
Events can legitimately flow in both directions without introducing unwanted dependencies between the container and the clients. In fact, allowing the container to receive events from the clients is a great way to minimize these dependencies. They provide a path for loose coupling precisely so that the container will be able to remain ignorant of what the clients actually are while still communicating with them. As long as the events in question are defined by the container, not by the clients.

## Develop layers first having in mind transition to Dependency Inversion principle and Inversion of Control at a later sta

By : Suresh Kumar Mukhiya
Date : March 29 2020, 07:55 AM
hope this fix your issue You can set up "poor man's dependency injection", using this kind of structure:
code :
``````public class MyEndClass
{

public MyEndClass(IDependency dependency)
{
this.dependency = dependency;
}

// temporary constructor until we introduce IoC
public MyEndClass() : this(new Dependency())
{
}
}
``````

## Inversion of Control, Dependency Inversion, and Service Locator difference clarification

By : CANZ
Date : March 29 2020, 07:55 AM
I hope this helps . Yes, you are correct.
SL is typically used inside frameworks to be able to locate all services. From the developers point of view they are just using dependency injection as the framework hides the service location. A typical example is ASP.NET MVC where you can use DI in your controllers. ASP.NET uses service location internally through the DependencyResolver class to allow you to use DI.

## Object is not null and not undefined. What is better - double inversion `!!` or strict equillity `!==` in JavaScript

By : lang
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further There isn’t any particularly good reason to ever use if (!!obj), as it’s equivalent to if (obj). !!obj and obj !== null && obj !== undefined do different things, though, and you should use whichever’s most appropriate.
obj !== null && obj !== undefined (surprise, surprise) results in false for null and undefined. !!obj results in false for anything falsy, including null, undefined, '', 0, NaN, and false.

## double values closed under inversion

By : sukhdev roy
Date : March 29 2020, 07:55 AM
it should still fix some issue using bisection search, I found the interval of double values that is invariant under 2x inversion
code :
``````value == 1.0 / (1.0 / value)
``````
``````[5.562684646268010E-309 ... 1.7976931348623151E308]
``````