function invert(out, a) {

    var aa = a[0];
    var ac = a[2];
    var atx = a[4];
    var ab = a[1];
    var ad = a[3];
    var aty = a[5];

    var det = aa * ad - ab * ac;
    if (!det) {
        return null;
    }
    det = 1.0 / det;

    out[0] = ad * det;
    out[1] = -ab * det;
    out[2] = -ac * det;
    out[3] = aa * det;
    out[4] = (ac * aty - ad * atx) * det;
    out[5] = (ab * atx - aa * aty) * det;
    return out;
}
Clone a new matrix.
@param {Float32Array|Array.<number>} a