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()
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
You can use bind for this.
recursiveDeterminantMatrix(this.cof(matrix, 0, i).bind(this));