function adjoint$2(out, a) {
    // Caching this value is necessary if out == a
    var a0 = a[0];
    out[0] = a[3];
    out[1] = -a[1];
    out[2] = -a[2];
    out[3] = a0;
    return out;
  }
Calculates the adjugate of a mat2

@param {mat2} out the receiving matrix
@param {ReadonlyMat2} a the source matrix
@returns {mat2} out