isIdentity(epsilon=0) {
        if (this._width !== this._height) {
            return false;
        }
        for (let c = 0; c < this._width; c++) {
            for (let r = 0; r < this._height; r++) {
                let i = (this._width*r + c)*2;
                let dr = Math.abs(this._buffer[i] - (r === c ? 1 : 0));
                let di = Math.abs(this._buffer[i+1]);
                if (Math.max(dr, di) > epsilon) {
                    return false;
                }
            }
        }
        return !this.hasNaN();
    }
Determines if the matrix is an identity matrix.
@param {!number} epsilon
@returns {!boolean}