trpfrog/InverseMatrix.html

## InverseMatrix.html
<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <link rel="shortcut icon" href="favicon.ico">
    <script type="text/javascript" src="./InverseMatrix.js"></script>
    <style>
      body{ margin: 2em; font-size: 3em;}
      input{ font-size: 1em; text-align: center; width: 3em;}
      button{ font-size: 0.8em; }
    </style>
    <script>
      function inputArea (id){
        html = '<input type="text" id="'+id+'" >';
        document.write(html);
      }
      function readArea (id){
        html = '<input type="text" id="'+id+'" readonly="readonly">';
        document.write(html);
      }
      function calc(){
        var aa = parseFloat(document.getElementById("aa").value);
        var ab = parseFloat(document.getElementById("ab").value);
        var ac = parseFloat(document.getElementById("ac").value);
        var ba = parseFloat(document.getElementById("ba").value);
        var bb = parseFloat(document.getElementById("bb").value);
        var bc = parseFloat(document.getElementById("bc").value);
        var ca = parseFloat(document.getElementById("ca").value);
        var cb = parseFloat(document.getElementById("cb").value);
        var cc = parseFloat(document.getElementById("cc").value);

        var matrix = createMatrix(aa,ab,ac,ba,bb,bc,ca,cb,cc);
        var det = getDet(matrix);

        matrix = getInverseMatrix(matrix);

        document.getElementById("aaR").value = matrix[0][0];
        document.getElementById("abR").value = matrix[0][1];
        document.getElementById("acR").value = matrix[0][2];
        document.getElementById("baR").value = matrix[1][0];
        document.getElementById("bbR").value = matrix[1][1];
        document.getElementById("bcR").value = matrix[1][2];
        document.getElementById("caR").value = matrix[2][0];
        document.getElementById("cbR").value = matrix[2][1];
        document.getElementById("ccR").value = matrix[2][2];
        document.getElementById("det").value = det;
      }
    </script>
</head>

<body>
  <h1 style="font-size: 1em;"> 逆行列計算機 </h1>
  <p>
    <table>
      <tr>
        <td></td>
        <td><script>inputArea("aa");</script></td>
        <td><script>inputArea("ab");</script></td>
        <td><script>inputArea("ac");</script></td>
      </tr>
        <td>A &nbsp; =　</td>
        <td><script>inputArea("ba");</script></td>
        <td><script>inputArea("bb");</script></td>
        <td><script>inputArea("bc");</script></td>
      <tr>
      </tr>
        <td></td>
        <td><script>inputArea("ca");</script></td>
        <td><script>inputArea("cb");</script></td>
        <td><script>inputArea("cc");</script></td>
      <tr>
        <td></td>
        <td style="font-size: 2em;">　</td>
        <td style="color: gray; font-size: 0.8em;">
          ↓<button onclick="calc()">計算</button>
        </td>
        <td></td>
      </tr>
      <tr>
        <td></td>
        <td><script>readArea("aaR");</script></td>
        <td><script>readArea("abR");</script></td>
        <td><script>readArea("acR");</script></td>
        <td>　　1</td>
      </tr>
        <td>A<sup>-1</sup> =　</td>
        <td><script>readArea("baR");</script></td>
        <td><script>readArea("bbR");</script></td>
        <td><script>readArea("bcR");</script></td>
        <td>　×──</td>
      <tr>
      </tr>
        <td></td>
        <td><script>readArea("caR");</script></td>
        <td><script>readArea("cbR");</script></td>
        <td><script>readArea("ccR");</script></td>
        <td>　&nbsp;<input type="text" id="det" readonly="readonly" style="width:2em"></td>
    </table>
  </p>
</body>

## InverseMatrix.js
function hasInverseMatrix(matrix){
	return getDet(matrix)!=0
}

function getInverseMatrix(matrix){
	let det = getDet(matrix);

  //逆行列の初期化
  let inverse = new Array(3);
  for(i=0;i<inverse.length;i++){
   	inverse[i] = new Array(3).fill(0);
  }

  for(let i=0;i<3;i++){
		for(let j=0;j<3;j++){
 			inverse[i][j] = getCofactor(i,j,matrix);
    }
  }
  inverse = transpose(inverse);
	multiply(det,matrix)
  return inverse;
}

function createMatrix(aa,ab,ac,ba,bb,bc,ca,cb,cc){
	return [[aa, ab, ac],
    			[ba, bb, bc],
    			[ca, cb, cc]];
}

function multiply(scalar,matrix){
  for(let i=0;i<matrix.length;i++){
		for(let j=0;j<matrix.length;j++){
 			matrix[i][j] *= scalar;
    }
  }
  return matrix;
}

function getCofactor(i,j,matrix){
	let elements = [0,0,0,0];
  let x = 0; //カウンタ

  for(let p=0;p<3;p++){
    if (p==i) continue;
		for(let q=0;q<3;q++){
 			if (q==j) continue;
      elements[x] = matrix[p][q];
      x++;
    }
  }
  matrix =  [[elements[0],elements[1]],
    			[elements[2],elements[3]]];

	return getDet(matrix)*((i+j)%2==0 ? 1 : -1);
}

function transpose(matrix){
  //2次元配列の初期化
  let transposed = new Array(matrix.length);
  for(i=0;i<transposed.length;i++){
    transposed[i] = new Array(matrix.length).fill(0);
  }
  //転置
 	for(let i=0;i<3;i++){
		for(let j=0;j<3;j++){
      transposed[i][j] = matrix[j][i];
    }
  }
  return transposed;
}

function getDet(matrix){
  if(matrix.length==3){
    let det = 0;
    det += matrix[0][0]*matrix[1][1]*matrix[2][2];
    det += matrix[1][0]*matrix[2][1]*matrix[0][2];
    det += matrix[0][1]*matrix[1][2]*matrix[2][0];
    det -= matrix[2][0]*matrix[1][1]*matrix[0][2];
    det -= matrix[0][0]*matrix[1][2]*matrix[2][1];
    det -= matrix[0][1]*matrix[1][0]*matrix[2][2];
    return det;
  }else if(matrix.length==2){
    let det = 0;
    det += matrix[0][0]*matrix[1][1];
    det -= matrix[0][1]*matrix[1][0];
    return det;
  }
}
	<!DOCTYPE html>
	<html>

	<head>
	<meta charset="utf-8">
	<link rel="shortcut icon" href="favicon.ico">
	<script type="text/javascript" src="./InverseMatrix.js"></script>
	<style>
	body{ margin: 2em; font-size: 3em;}
	input{ font-size: 1em; text-align: center; width: 3em;}
	button{ font-size: 0.8em; }
	</style>
	<script>
	function inputArea (id){
	html = '<input type="text" id="'+id+'" >';
	document.write(html);
	}
	function readArea (id){
	html = '<input type="text" id="'+id+'" readonly="readonly">';
	document.write(html);
	}
	function calc(){
	var aa = parseFloat(document.getElementById("aa").value);
	var ab = parseFloat(document.getElementById("ab").value);
	var ac = parseFloat(document.getElementById("ac").value);
	var ba = parseFloat(document.getElementById("ba").value);
	var bb = parseFloat(document.getElementById("bb").value);
	var bc = parseFloat(document.getElementById("bc").value);
	var ca = parseFloat(document.getElementById("ca").value);
	var cb = parseFloat(document.getElementById("cb").value);
	var cc = parseFloat(document.getElementById("cc").value);

	var matrix = createMatrix(aa,ab,ac,ba,bb,bc,ca,cb,cc);
	var det = getDet(matrix);

	matrix = getInverseMatrix(matrix);

	document.getElementById("aaR").value = matrix[0][0];
	document.getElementById("abR").value = matrix[0][1];
	document.getElementById("acR").value = matrix[0][2];
	document.getElementById("baR").value = matrix[1][0];
	document.getElementById("bbR").value = matrix[1][1];
	document.getElementById("bcR").value = matrix[1][2];
	document.getElementById("caR").value = matrix[2][0];
	document.getElementById("cbR").value = matrix[2][1];
	document.getElementById("ccR").value = matrix[2][2];
	document.getElementById("det").value = det;
	}
	</script>
	</head>

	<body>
	<h1 style="font-size: 1em;"> 逆行列計算機 </h1>
	<p>
	<table>
	<tr>
	<td></td>
	<td><script>inputArea("aa");</script></td>
	<td><script>inputArea("ab");</script></td>
	<td><script>inputArea("ac");</script></td>
	</tr>
	<td>A   =　</td>
	<td><script>inputArea("ba");</script></td>
	<td><script>inputArea("bb");</script></td>
	<td><script>inputArea("bc");</script></td>
	<tr>
	</tr>
	<td></td>
	<td><script>inputArea("ca");</script></td>
	<td><script>inputArea("cb");</script></td>
	<td><script>inputArea("cc");</script></td>
	<tr>
	<td></td>
	<td style="font-size: 2em;">　</td>
	<td style="color: gray; font-size: 0.8em;">
	↓<button onclick="calc()">計算</button>
	</td>
	<td></td>
	</tr>
	<tr>
	<td></td>
	<td><script>readArea("aaR");</script></td>
	<td><script>readArea("abR");</script></td>
	<td><script>readArea("acR");</script></td>
	<td>　　1</td>
	</tr>
	<td>A<sup>-1</sup> =　</td>
	<td><script>readArea("baR");</script></td>
	<td><script>readArea("bbR");</script></td>
	<td><script>readArea("bcR");</script></td>
	<td>　×──</td>
	<tr>
	</tr>
	<td></td>
	<td><script>readArea("caR");</script></td>
	<td><script>readArea("cbR");</script></td>
	<td><script>readArea("ccR");</script></td>
	<td>　 <input type="text" id="det" readonly="readonly" style="width:2em"></td>
	</table>
	</p>
	</body>
	function hasInverseMatrix(matrix){
	return getDet(matrix)!=0
	}

	function getInverseMatrix(matrix){
	let det = getDet(matrix);

	//逆行列の初期化
	let inverse = new Array(3);
	for(i=0;i<inverse.length;i++){
	inverse[i] = new Array(3).fill(0);
	}

	for(let i=0;i<3;i++){
	for(let j=0;j<3;j++){
	inverse[i][j] = getCofactor(i,j,matrix);
	}
	}
	inverse = transpose(inverse);
	multiply(det,matrix)
	return inverse;
	}

	function createMatrix(aa,ab,ac,ba,bb,bc,ca,cb,cc){
	return [[aa, ab, ac],
	[ba, bb, bc],
	[ca, cb, cc]];
	}

	function multiply(scalar,matrix){
	for(let i=0;i<matrix.length;i++){
	for(let j=0;j<matrix.length;j++){
	matrix[i][j] *= scalar;
	}
	}
	return matrix;
	}

	function getCofactor(i,j,matrix){
	let elements = [0,0,0,0];
	let x = 0; //カウンタ

	for(let p=0;p<3;p++){
	if (p==i) continue;
	for(let q=0;q<3;q++){
	if (q==j) continue;
	elements[x] = matrix[p][q];
	x++;
	}
	}
	matrix = [[elements[0],elements[1]],
	[elements[2],elements[3]]];

	return getDet(matrix)*((i+j)%2==0 ? 1 : -1);
	}

	function transpose(matrix){
	//2次元配列の初期化
	let transposed = new Array(matrix.length);
	for(i=0;i<transposed.length;i++){
	transposed[i] = new Array(matrix.length).fill(0);
	}
	//転置
	for(let i=0;i<3;i++){
	for(let j=0;j<3;j++){
	transposed[i][j] = matrix[j][i];
	}
	}
	return transposed;
	}

	function getDet(matrix){
	if(matrix.length==3){
	let det = 0;
	det += matrix[0][0]matrix[1][1]matrix[2][2];
	det += matrix[1][0]matrix[2][1]matrix[0][2];
	det += matrix[0][1]matrix[1][2]matrix[2][0];
	det -= matrix[2][0]matrix[1][1]matrix[0][2];
	det -= matrix[0][0]matrix[1][2]matrix[2][1];
	det -= matrix[0][1]matrix[1][0]matrix[2][2];
	return det;
	}else if(matrix.length==2){
	let det = 0;
	det += matrix[0][0]*matrix[1][1];
	det -= matrix[0][1]*matrix[1][0];
	return det;
	}
	}