I am trying to make a matrix class. The cof() function is not working when I am using it as a method and showing this error.
practice:47 Uncaught TypeError: Cannot read property 'cof' of undefined.

But when I am using it inside det() method as a function it is working perfectly. Can anyone explain why this is happening?

class Matrix{
 
 constructor(matrix){
     this.matrix = matrix
 }   
 
 cof(matrix = this.matrix, i, j) {
    let cofMat = matrix.map(row =>
      row.filter((_, colIndex) => j !== colIndex)
    )
    cofMat.splice(cofMat[i],1)
    return cofMat
  }
     
 det(matrix = this.matrix) {
  let validInput = true;

  //input validation
  let columnLength = matrix.length;
  matrix.forEach((row) =>
    row.length === columnLength ? (validInput = true) : (validInput = false)
  );
  if (!validInput) return "Input a valid n*n matrix";

  // determining the matrix using 1st row.

  // This function is not working properly as a method

  function cof(matrix, i, j) {
    let cofMat = matrix.map(row =>
      row.filter((_, colIndex) => j !== colIndex)
    )
    cofMat.splice(cofMat[i],1)
    return cofMat
  }

  function recursiveDeterminantMatrix(matrix) {
    if (matrix.length === 2 && matrix[0].length === 2) {
      let result = matrix[0][0] * matrix[1][1] - matrix[0][1] * matrix[1][0];
      return result;
    } else {
      let answer = 0;
      for(let i =0; i< matrix.length; i  ) {
        let cofactor =
          (-1) ** i *
          matrix[0][i] *
          recursiveDeterminantMatrix(this.cof(matrix, 0, i));
        answer  = cofactor;
      };
      return answer;
    }
  }

  return recursiveDeterminantMatrix(matrix);
 }  
}

let matrix = [[1,2,3],[4,5,6],[7,8,8]];

let mat = new Matrix(matrix).det()

CodePudding user response：

When the recursiveDeterminantMatrix function executes, this does not evaluate to the instance of the class, because it's not a method, just a plain function.

You could save the instance of the class in a self variable for proper use in the inner function.

det(matrix = this.matrix) {
 const self = this;

 // ...

 function recursiveDeterminantMatrix(matrix) {
   if (matrix.length === 2 && matrix[0].length === 2) {
     let result = matrix[0][0] * matrix[1][1] - matrix[0][1] * matrix[1][0];
     return result;
   } else {
     let answer = 0;
     for(let i =0; i< matrix.length; i  ) {
       let cofactor =
         (-1) ** i *
         matrix[0][i] *
         recursiveDeterminantMatrix(self.cof(matrix, 0, i));
       answer  = cofactor;
     };
     return answer;
   }
 }

 return recursiveDeterminantMatrix(matrix);
} 

For more information about this keyword, please check the MDN Docs

CodePudding user response：

You can use bind for this.

recursiveDeterminantMatrix(this.cof(matrix, 0, i).bind(this));