set(rowIndex, columnIndex, value) { // eslint-disable-line no-unused-vars
                throw new Error('set method is unimplemented');
            }
Sets a given element of the matrix. mat.set(3,4,1) is equivalent to mat[3][4]=1
@abstract
@param {number} rowIndex - Index of the row
@param {number} columnIndex - Index of the column
@param {number} value - The new value for the element
@return {Matrix} this